Plumbing FAQ for Reef Tanks

(or 101 ways to flood your house!)

The information in this document is based upon several sources. Much of it is based upon observations of different plumbing setups in various reef tanks, as well as my own experiences. In addition, some info comes from the various Internet sources, books, and plumbing catalogs and web-sites.

The easiest way to handle plumbing for a reef tank is to have none at all. Small sump-less systems incorporating HOTB (Hang-on-the-back) skimmers (or no skimmer), and using ordinary power-heads for circulation may require no plumbing at all. On the other hand, large systems may incorporate multiple tanks plumbed together with multi-chambered sumps, skimmers, calcium reactors, surge devices, internal circulation systems, dosing pumps, spray bars, etc. Most systems will fall somewhere in-between.

11.1  Sumps

Most larger reef systems will include a sump. A sump is a water reservoir which is at a lower level than that of the tank.  Gravity is used to cause water to drain from the main tank to the sump.  A pump is used to move water from the sump back to the tank.  This creates a continuous flow where all water in the system passes through the sump.

11.1.1  Advantages

There are several advantages to having a sump versus not having one:

Basically a 50 gallon tank with a 50 gallon sump has more water in it then a 100 gallon reef system, but only has the same calcium consumption rate, nitrate production rate, # of watts of light, etc as a 50 gallon tank.

3. Additional gas exchange: The overflow system which transfers water from the tank to the sump will usually provide a great amount of aeration to the water. This will help keep oxygen levels high.
4. Surface skimming: Organic compounds which are attracted to air-water interfaces will form in your reef tank. These will show up as an oily film on the water surface. The overflow systems used to supply the sump with water collect their water from the top of the tank, which will break up this film. Since these compounds are attracted to air-water interfaces, your protein skimmer can efficiently remove them.
5. Additional circulation: The water flow from the sump to the tank and back down will help with circulation in your tank. The pump doing the returning is not in the main display tank, so there will be one less ugly pump in the tank. In addition, non-submersible pumps can be used. Non-submersible pumps are available which are more powerful than any of the submersible powerheads. They will also usually heat the water less than submersible pumps of a similar size, since some of their generated heat will radiate to the air rather than into your aquarium water.
6. Constant water level. Instead of the water level going down in the main tank due to evaporation, that level will remain constant, while the level in the sump lowers instead.
7. Easy place to add additives. If you add any chemicals to the sump, they will have a chance to be diluted in the water in the sump before any of the creatures in the main tank are affected by them.
8. Ease of working on the tank without disturbing the inhabitants. You can remove some amount of water for water changes without affecting the level in the main tank, and while leaving all circulation active in the system. Plumbing changes and cleaning can be done by first shutting off the return pump from the sump. The inhabitants of the display tank won't even know anything is going on.
9. Protein Skimmers:  You will have a much larger set of usable protein skimmers to choose from.

11.1.2  Downsides

"Wow, that's great! Any downsides?"

A couple.  You've got to have a place to put the sump of course, and this can be difficult with some stands.  There's also some intricacy to plumbing them that can increase the chances of water spills.  You've also got to pay money for the sump and return pump of course.

11.1.3  Sump Setup

"I'm sold anyway. How do I set this up?"

You need to make some decisions:

11.1.3.1  "What should I use for the sump?"

Any container capable of safely holding saltwater that will fit in your desired location will work.  Probably the best (and most expensive option) is a clear acrylic tank.  The acrylic is strong and light, relatively easy to drill, and can be made in any size or shape.  You can either make the sump yourself, have anyone who makes acrylic aquariums make one for you, or buy pre-built units. Some of the commercial acrylic wet-dry filters can have the filter media and other undesired components removed for use with a reef.

The next-best container to use is a standard glass aquarium.  They are significantly cheaper than acrylic sumps.  Holes can often be drilled by your local fish store (LFS).  The relative fragility is a downside.  For instance, I'd be very nervous about putting the big heavy titanium heat exchanger from a drop-in chiller in a glass sump.

Various non-transparent plastic containers can be used as well.  For those setting up very large sumps, these may be the best choice.  PVC, fiberglass, or other large containers made for agricultural use are commonly used for sumps of more than 100 gallons.  You should use either containers that are targeted for aquacultural use, or those that are approved by the FDA for drinking-water storage.

For those on a budget, various Rubbermaid containers not made for water usage can be used for sumps.  However, there is a danger that nasty chemicals such as anti-fungal compounds may have been added to the plastics during manufacturing and that these will leach into your tank.  There is no way to tell if a particular container is safe or not.  I have used these for sumps without incident, but others might not be so lucky.  In addition, they have other negative properties, such as the fact that they bow when filled with water, which might make it impossible to close the doors of your aquarium stand. This also makes it impossible to install baffles or other rigid dividers into the sump. On the plus side, they are super-cheap, can be trivially drilled, and may be the only way to fit a sump of decent volume into some stands (especially since they can be bent when you're squeezing them through the stand doors).

Plywood sumps constructed in the same fashion as plywood aquariums might also work well.  They would be rigid and un-fragile like acrylic, but also cheap to build.  A local fish store uses one lined with fiberglass resin.  It's also possible to use wooden containers combined with plastic pond liners.  OTOH, I have received a warning telling of a Tetra pond liner used in a sump causing massive saltwater fish losses.

If it is not possible to fit a sump of the volume you desire through the doors of your stand, it is possible to chain together 2 smaller sumps.  Put a bulkhead on the end of each sump and use a piece of PVC to attach them together.  You should use a larger diameter of pipe for this than you use in the rest of your system.  Larger diameters used here will keep the water level between the 2 sumps closer to equal.

11.1.3.2  "Why would I want to drill my sump?"

The most common way to attach an external return pump to a sump is to drill a hole in the side of it and attach a bulkhead into this hole. You then run pipe from the bulkhead to the pump.

11.1.3.3  "What is a Bulkhead?"

A bulkhead is a plumbing part used to mate a container with PVC pipe. You cut an appropriate-sized hole in the container and insert the bulkhead fitting and tighten the bulkhead caps. You can then mate the bulkhead with threaded fittings (if it is a threaded bulkhead) or just glue in a piece of PVC pipe (if it is a SLIP-type bulkhead)

11.1.3.4  "How do I return water from the sump to the tank?"

You need a pump for this.  The pump must be capable of moving a high enough volume of water up from the sump to the tank.  A common rule of thumb is to try to have water volume equal to the entire contents of the tank cycle through the sump 4 times per hour.  Even more than this is better, since it will provide more circulation in the main tank.  While it is possible to buy pumps capable of moving as much water as you could possibly want, providing a matching amount of water flow back from the tank to the sump may be a problem.

For small systems, you can use submersible powerheads for the return.  The larger models, such as Aquaclear 802 and larger RIO models can do a fine job. One drawback of using these powerheads is that their outlets aren't set up to easily connect to standard sizes of PVC fittings.

For larger systems, or when there is a larger height difference to overcome, or when large flow rates are desired, external non-submersible pumps are the way to go.  The cheapest external pumps will start at prices around $100 and can handle flow rates of around 500 GPH at a decent height.  At the upper end there are pumps costing >$300 and moving thousands of gallons per hour.  For very large systems or systems pumping a high distance, even more powerful pumps are available.  There are some pumps marketed for swimming pool usage which can be used safely in saltwater and which can move ungodly amounts of water.

When comparing pump models, be sure to look at how they perform at a head pressure similar to the height of your tank above your sump.  Some pump manufacturers have different models for pressure and circulation applications.

Your pump needs to be plumbed so that it can draw water from the sump and pump it into the main tank.  For the submersible powerheads, this means just putting the powerhead in the sump and running pipe and/or tubing from the powerhead outlet up to the tank.

For an external pump, the pump needs to be put somewhere dry.  The inlet side of the pump needs access to the water in the sump.  Generally, the pump should be placed at a level that would be underwater if it were in the sump, and be attached through a bulkhead connector to a side of the sump.  The outlet side of the pump will be connected to pipe and/or tubing which leads to the top of the tank.

Most pumps used in aquarium systems are not capable of self-priming.  What this means is that while they can PUSH water up just fine, they can't PULL it up through an air-filled pipe. So, for instance, if you are using a non-submersible pump with a sump which cannot be drilled for a bulkhead fitting, and you plumb the inlet to go up over the side of the sump and down into the water, the pump will not work.  However, if the pipe on the inlet side were somehow filled with water, it would work.  With the use of check valves on the outflow, and an initial manual priming, such a system could probably be made to work adequately, but I have no experience with such a setup.

So, you have plumbing leading from the sump to the inlet of your pump.  The outlet side of the pump needs to be plumbed to go up to the tank.  This should be as direct of a path as possible, with as few bends as possible.  Flexible vinyl tubing is useful here, since it may make it possible to avoid some elbows which slow down flow.  Be careful if using tubing that it isn't plumbed in such as way as to cause the tubing to kink.

The end of this system needs to end up somewhere where it can put water into your tank.  Unless you're into bubbles and salt-spray, you probably don't want it to end up above your tank and pour water straight down.  There are various ways to construct the output side of your return plumbing:

Whatever method you use to direct the return flow from your pump back to the tank, you should pay careful attention to two issues in order to prevent leaks:

1. Make sure that the return is securely mounted and that all tubing is secured.  If the return plumbing is disrupted in some way or the return line falls out of the tank, you could easily end up with a fairly big water spill.
2. Watch out for siphon effects!  If your return line is underwater in the display tank, water will siphon down the return line when the pump turns off (due to power outages, pump failure, etc).  Water will siphon out of the main tank into the sump until the water level in the main tank drops below that of the return line.  If the return line is just an inch or so below the water line, this may not be a problem.  With a return line plumbed to a vertical spray bar however, the entire tank could drain due to this effect.  The possible volume of water siphoned in this manner can be reduced by drilling "siphon-break" holes in the return plumbing just below the water line.  These will cause air to be sucked in with the siphoning water, breaking the siphon.  These holes should be fairly large and should be checked often for blockage by encrusting organisms.

In general, you should check your plumbing for loss-of-power vulnerabilities occasionally.  Turn off your pumps and observe what happens.  Be prepared to switch them back on quickly if if looks like there could be a possible spill.

11.1.3.5  "How big should my sump be?"

All else being equal, a larger sump is better than a smaller one.  An ideal sump is as large or larger than the tank it is being used with.  The extra water volume contained within such a sump will go along way towards providing stable water chemistry.  Unfortunately, this ideal is not usually practical, unless the sump is plumbed remotely (such as in a basement or garage).

At the minimum, your sump needs to be large enough to hold all the equipment you intend to house in it.  It also needs to have enough volume to contain the water which will overflow into it during a power failure.

It is possible to reasonably estimate the amount of excess water area needed in a sump to handle a power failure or other shutdown.  All you need to do is figure out how much water will return to the sump in this case.  Summing the following quantities can give you a rough estimate:

1. Figure out how many inches the water level in the tank will fall when power goes out. This is the maximum of the number of inches of water above the lowest point of the surface skimming part of the overflow and the number of inches of water above the lowest point of the pump return (or above the siphon drain hole in the pump return) multiplied by the total gallon capacity of your tank, and then divided by the height of the tank. So, on a 72"x18"x24" tall tank (a standard 125G), if the water level may drop by 1" when power is removed, 5.2 g of water may come back down the overflow and return pipe.
2. The amount of water present in the piping at the time of the power removal. For instance, 6' of 1" pipe can be over-estimated to hold one gallon of water. The same length of 2" pipe might hold 4 gallons.
3. The amount of water present in the skimmer or other equipment.

11.1.3.6  "How do I get water from the tank to the sump?"

While the sump-to-tank circulation is handled by actively pumping the water up, the path to the sump is generally handled by a passive gravity feed.   Through gravity, all water above a certain level in the main tank is set up to drain into the sump.  This system is called an overflow, since water overflows and falls to the sump.

It is very important to have the water which ends up in the sump drawn from the very surface of the water in the tank. Your tank will have organic compounds produced in it which are attracted to air-water interfaces (such as the top of your water column), resulting in a kind of oily film forming on the water surface.  If left alone, this film may look unsightly and reduce the amount of oxygen in your water.  These films are easily removed by protein skimming, since they are attracted to air-water interfaces.  If you are running skimmerless and attempting to bio-assimilate most of your organic waste, it is also important to break up this film so that some of the compounds have the possibility of being broken down or being absorbed by carbon.

The simplest practical system is to have one or more holes drilled into the back (or front, or sides), of the main tank.  Fit bulkhead fittings into these holes.  On the outside of the tank, attach appropriate piping and tubing so that water can flow down into your sump.  All water at the level of the drilled hole or higher will flow down this plumbing into your sump.  If everything is appropriately sized, this will result in the amount of water entering the sump being equal to that leaving it, which is a good thing.

With this setup, you will most likely want your water level in the main tank to be higher than the level at which the hole is drilled. This is easily accomplished by adding a 90º elbow to the inside-the-tank portion of the bulkhead and attaching a small length of PVC pipe.  Install the elbow and pipe facing up, and water will only drain from the height of the top of this short piece of PVC.

This setup is a very good one, and will cost you the price of having your tank drilled, plus a bulkhead fitting and misc. plumbing supplies.  It will be reasonably quiet and takes up little space.  The intake of this system should be covered in some way to prevent fish and larger inverts from falling into it and either clogging your plumbing or ending up in the sump (and maybe pureed by your return pump).  One of the black plastic bulkhead overflow strainers available is good for this.  Other possibilities are egg crate, various screens, etc.

Another possibility for a back-drilled overflow is to enclose the hole in a small "skimmer box".  This is a box which surrounds the hole, with its open top at the desired water level.  Water which overflows the box will exit through the drilled hole.  You can make one of these with glass and silicone, though plastic with carved "teeth" is better.  This is similar to the normal "reef-ready" drilled overflows that commercial tanks come with.

The normal "reef-ready" aquarium with built-in overflows is set up with a drilled bottom.  The holes in the bottom are surrounded by "walls" which rise to near the top of the tank.  Water which rises over the level of these walls falls over the sides and down the holes. Usually the chamber around the hole is plastic, with "teeth" cut into the top of it to allow water to flow and prevent creatures larger than the gap between the teeth from falling down the overflow.  Usually these tanks have one overflow in each of the back corners. These tanks require that the stand be open in the area where the holes is.  An advantage of the bottom-drilled overflow is that if the sump is directly underneath the tank, it is possible to have an absolutely straight path from the overflow to the sump without any bends or elbows.

11.1.3.7  "How do I drill my tank?"

Look for a local aquarium store or glass place that will do it for you.  Prices of $10 or $20 per hole are typical.

11.1.3.8  "I can't or don't want to get my tank drilled! What can I do?"

You can use a siphon box, either buying or building one.  A siphon box is a somewhat complicated system that causes water above a certain level in your tank to get siphoned out to the sump.

When 2 water reservoirs are connected by a water-filled pipe, water will flow between them to keep the levels the same in both reservoirs.  This principle can be used to make an overflow.

The simplest possible safe system is as follows:

One reservoir (a box with no top) sits inside the tank. Another reservoir sits behind the tank.  A clear plastic tube shaped like a "U" is inserted upside down joining the two boxes.  Both boxes have water poured into them.  All the air is sucked out of this tube by a piece of airline tubing.  At that point, the water level will equalize between the two boxes.  Water that rises above the level of the box inside the tank will flow from that box into the back one to equalize the levels.  If a way is added to get that water out of the back box and into the sump, a continuous flow will have been achieved.  This can be accomplished by drilling a hole in the bottom of that back box.  Insert a bulkhead into this hole, and plumb the output side down to the sump.  Plumb the other side with a piece of pipe that goes straight up, with it's top ABOVE the bottom ends of the U tube, and BELOW the level of the top of the 2 boxes.

When water is added to the main tank as a result of being pumped from the sump, it will rise and overflow over the edges of the box inside the tank.  This will cause the water level to rise to equalize in the other box through the U-tube.  Eventually, the water level in both boxes will rise up to the top of the pipe that was added in the rear box.  Water will then begin flowing into this pipe, through the bulkhead, and down to your sump.  If the pump is turned off, water will stop flowing between the 2 boxes and thus to your sump.  Since the outflow pipe end is ABOVE the ends of your U-tube, enough water will remain in both boxes so that the u-tube remains full of water.   When the pump starts pumping again, the siphon will still be active and water will flow properly.

Most commercial designs are a little more complicated than this, omitting the standpipe in the rear and instead using a divider to keep part of the rear chamber flooded in the event of power outage.  I'm not sure if there is any advantage to this.  If you get one of these overflows, it is VERY important to place the end(s) of the U-tube(s) on the side of the rear chamber that doesn't have the hole, or things won't start up correctly if power is lost.

When setting up or changing your sump/overflow system it is extremely important to turn the power on and off and make sure that everything works right in the event of a power outage.

Some of the commercial systems don't use the U-tubes, but rather build a siphon into the box.

The main problems people have with these siphon systems is air build-up in the siphon tube(s).  If enough air builds up in there, it can slow or halt the water flow, causing a rise in the water level of the tank and a possible flood. Bubble buildup can be reduced by carefully sizing the return pump and overflow tubes.  When there are more tubes than are needed for the given flow rate, bubbles build up more rapidly because of the slower flow velocity. When there is just enough flow available, the faster water movement will send bubbles over and out the tubes instead of letting them build up at the top of the tube.  Also, having fewer bubbles present in the tank will help.

It is also possible to setup a system for automatically removing air.  If a small powerhead with a Venturi input is set in the rear chamber of the overflow box, and a piece of airline tubing run from the Venturi input to an airline valve carefully sealed to a hole drilled at the top of the U-tube, the suction of the Venturi valve will pull air out of the tube as it builds up.  With the pump sitting in the back of the overflow system, it will not break the siphon by pulling all the water out, since the water it pulls will be replaced via the siphon action.  It is also possible to use a peristaltic or diaphragm pump to suck the air out.

These overflow systems do work, but IMHO, should only be used as a last resort when drilling is impossible, and should particularly be avoided on larger tanks.

11.2  Working with PVC

Most reef plumbing is done with ordinary PVC pipe, available cheap at your local HW store. White schedule 40 pipe is what I have seen most people using. There are a large number of fittings available for different purposes.

Most fittings connect to the pipe (or each other) using either "SLIP" or "threaded connections".  The Slip connection is just a larger diameter hole which an appropriately-sized section of pipe is stuffed.  The fact that it says "Slip" doesn't mean that you just slip the pipe in and you're done -- if you do this, it will leak like a sieve.  What you do is use PVC cement to permanently glue the pieces together.  Make sure both sides of the join are clean, coat both with cement, and then press them together and turn a quarter-turn or so to make a good seal.  The cement will bond VERY quickly.

A threaded connection is used with fittings which have matching threads allowing one piece to be screwed into the other.  The smaller diameter threaded section ("male") is inserted into the larger diameter ("female") piece, and turned to screw them together.  However, there is more to it than this.  If they are just inserted dry, the joint will leak.  You need to use either Teflon pipe tape or pipe-joint compound to get a leak-free fit.  With the Teflon tape, you neatly wrap the mail threads with tape before screwing them in.   With the pipe joint compound, you coat the mail threads with the goop-like compound before screwing them in.  The pipe joint compound does not dry and maintains a sticky consistency.  The pipe joint compound is easier and faster to use, but messier than the tape.

Slip connections are permanent and can only be cut apart, while threaded ones can be unscrewed.  Slip fittings can be mated directly with PVC pipe, while threaded ones require adding threaded fittings to the pipe.  Generally you're better off using slip connections except where you might want to remove fittings, or when the part you wish to attach is threaded.

11.2.1  PVC Parts

At any store such as Home Depot, you'll find a lot of different fittings available, in different sizes and with different combinations of male, female, slip, threaded, etc.

11.2.2  Shopping Tips

Generally, most of your purchasing for plumbing supplies is going to be done at your local Home Depot or equivalent, rather than at your aquarium store.  If your aquarium store does sell tubing, pipe, fittings, etc, they will most likely have a smaller selection and higher prices than your local HW superstore.   Some parts, however, may be more easily obtained at a good aquarium store (I've never seen bulkhead fittings at Home Depot for instance).

11.2.3  Parts

Elbow

Used to join 2 lengths of pipe at an angle. There are 90º and 45º elbows.

 

Street Elbow

Similar to an elbow, except that one side of the elbow is the same diameter as pipe, so that a street elbow can be directly attached to another elbow or fitting without the need for a short length of pipe.

"T",Tee

joins 2 sections of pipe, for instance to split a flow into 2 paths. Some tees are reducing - they take an input of one diameter and split it into 2 of smaller diameter.

Bushing

Used to fit one size of pipe into a fitting intended for another size.

 

Cap

seals off the end of a piece of pipe.

 

Hose barb

provides a hookup for vinyl tubing.

 

Ball valve

A valve which allows adjusting flow or completely shutting it off. Usually white with a red turner.  Relatively course adjustments only.

 

Needle valve

Allows much finer adjustment of flow. Harder to find.

 

Union

connects 2 pieces of pipe so that they can be disconnected without rotating the pipe.  Uses an O-ring to seal the connection.  Important if you want to be able to take your plumbing system apart.

 

Union Ball-Valves

A ball valve combined with one or 2 unions. Allows you to shut off water flow across the valve and remove one side without spilling (too much) water.

 

Compression Fitting", Pipe Repairers

These are a white PVC fitting that allows a piece of pipe to be connected at each end.  Caps then screw down over the pipe ends, sealing with a rubber ring.  Unscrewing the caps allows you to take apart the plumbing.  One useful thing about these is that you can adjust how far into the fitting the pipe goes, allowing minor adjustments of length after the system is put together.

 

3 Way Valves

The valve controls how much goes to one side of a tee and how much to the other.

 

3 Way Motorized Valves

Motorized version of the above. A wavemaker can create back and forth flows without turning any pumps on or off. Expensive but said to be very nice.

 

Cage Fittings, Corner Tees

Tees with the 3 (or 4 or more) inputs meeting at a corner. Useful for building pvc structures, furniture, etc.

There is a whole family of PVC parts that attach to the OUTSIDE of PVC pipe using normal PVC glue.  You can use them for supporting pipes, etc.

11.2.4  Plumbing Tips

1. Use SLIP (insert) fittings instead of threaded ones wherever possible. The threaded fittings are a lot more likely to have leak problems and attaching fittings using pvc solvent is a lot faster than taping the threaded fittings.

2. Use pvc primer. The primer cleans the pipe and enhances the strength of the bond. If you've got a tendency to be sloppy, use the clear rather than the purple primer since the purple stuff can stain things easily.

3. Dry-fit things and make sure everything is the right length before gluing.

11.2.5  Misc

"How do I attach the output of my powerhead to pvc? It doesn't fit any standard size."

Assuming that the powerhead is going to be submerged (and thus, a little leakage is OK), use some vinyl tubing. You can find a size of tubing that will go over the powerhead outlet or inside it and also over or inside a piece of pipe (or you can attach it to a hose barb).

Vinyl tubing is softer and easier to stretch when warm. If you can almost-but-not-quite get it over the outlet of the powerhead, dip it into some boiling water for a little bit and then you'll probably get it on.

"How do I cut PVC pipe?"

You probably want a handheld pipe-cutter. It has a big cutting blade which is moved a little bit by a wheel every time you squeeze the handle. You can make clean cuts with a minimum amount of effort. Should cost you about $12 at the HW store. Such cutters for larger diameters of pvc are harder to find, but they exist (I have one that does 2" or greater diameter pipe). You can also use various table saws to cut pvc.

"How do I build an acrylic sump?"

Beyond the scope of this document. You can find various net archives discussing how to work with acrylic. If you can buy the acrylic cut to your dimensions, it's pretty much a no-brainer.

"How do I cut glass?"

Get your HW superstore to do it for you when you buy the glass. They probably won't even charge.

"What are some of the other ways to flood my house? You mentioned 101."

There's probably more than 101. Here's some:

1. Animals getting caught in overflow plumbing and clogging it Can be prevented by shielding the outflows.  Things like bags of carbon, filter sponges, etc can also end up blocking things.  If you're using a filter sponge in your overflow, make sure it doesn't get clogged and reduce the flow too much.
2. Leaks:  Most likely places for leaks are at bulkhead connections and threaded piping connections.  When setting up a new tank, you should get the bugs out of your plumbing before adding salt and animals.  The chance of leaks through a bulkhead can be reduced by using silicone around the fitting.  If you have a leaking joint that cannot be re-done, there are a few products that can fix the leak, including various epoxies, plumber's goop, silicone, etc.
3. Powerheads going amok. The big rio 2500 blowing water across your shallow long tank falls and ends up blowing straight up. The tubing falls off your return powerhead and it sprays water everywhere.  IMHO, powerhead suction cups are time bombs waiting to happen and should be avoided.
4. Un-minded water transfers: If the phone rings while you're pumping water from your SW reservoir to your tank, DON'T ANSWER IT!.
5. Unminded sink or RO unit: Be VERY careful with anything that is plumbed into your house's main water supply, because it has an infinite amount of water available to cause trouble. Instead of soaking your living room, you could flood your whole street!
6. Unexpected siphons: just because you turned off that powerhead before carrying a bucket of water upstairs doesn't mean that water can't still travel through the tubing attached to it.
7. Too much water in the system: Occasionally turn off your return pump and see how high the water level gets in the sump before it stops. Plumbing changes may effect this level.
8. Unexpected outcomes: Don't re-do any of your plumbing 20 minutes before catching the plane for your 2 week vacation in Palau.

11.3  Water Flow

Water flow is critical to the reef aquarium. It would be hard to overstate its importance. Water currents:

IMHO, most tanks probably would benefit from more water movement. An article by Richard Harker in Aquarium Frontiers compared water flow in people's reef tanks to several real reef areas. Most tanks had less water flow than he measured in Bonaire, a beautiful island in the Dutch Antilles which is known for its extremely GENTLE currents. Those aiming for a lagoon-type ecosystem may wish to aim for less severe currents though.

Different corals and other sessile invertebrates may react negatively to either high or low currents. Once your reef tank has been established and populated for a while, changes in water flow regime should be handled carefully - corals will have grown in forms influenced by the current surrounding them and may not appreciate large changes in that. Large hard corals such as acropora species may be the least tolerant of changes since they seem to tailor their skeletal growth to optimize it for the current and lighting conditions where they are growing. OTOH, even if you do nothing in your tank, the water flow regime will still change over time as coral growth modifies the flow patterns in the tank.

Excepting a few exotic devices, water flow in aquariums is provided by external or submersible pumps. These suck water in from an intake and push it back out through the outflow. They are commonly rated in GPH (gallons per hour) or GPM (gallons per minute) (or liters/hr or lt/minute in countries using more rational systems of units than the USA). Pumps moving 50GPH up 1000's of GPH and everywhere in-between are available.

A word about pump ratings - the rated GPH of a pump may be much higher than you'll actually see when really using the pump. Pumps will generally move significantly less water when pumping against gravity (many pumps quote their rating at various "feet of head", which lets you see how much water they can pump when working against 4 feet of gravity, for instance) They will also move less water when pushing through long sections of plumbing, or when their outflow is restricted. They may also move less water as they age.

When figuring out how to get the desired amount of current in your reef tank, you should first consider the return pump (in a system with a sump). Since this pump is generally located below the tank or in some other place out of sight, with just a return line visible in your tank, and since you're going to have it anyway, you should move as much water as practical with this pump. Limiting factors to the size of this pump are:

You should generally use the largest return pump possible after considering these factors. For a given GPH of flow, one larger pump usually does it cheaper and with less generated heat than N smaller pumps. If the chosen return pump generates too much flow in one area, you can always "T" it off into multiple lines returning to different portions of the tank.

If you need more water flow than your return pump can provide, or if you want more water flow to particular areas, or if you want to add variable water flow, you can add additional pumps. Often these take the form of submersible "powerheads"... smaller pumps which are completely sealed and have cords insulated with saltwater-safe insulation. These pumps have the advantages of having generally low purchase costs, being silent while running, and being simple to plumb. Adding a powerhead can be as simple as finding a spot on the aquarium glass to suction-cup it to, and the plugging it in.

11.4  Topics to be Added

Revision History:

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