Simple DIY Overflow

SIMPLE OVERFLOW

This description was written in 2003 and it's being copied and posted as is. I'll edit when I have time. I have made these devices so many times that it seems easy, but it probably doesn't look so easy.

First Principle: The aquarium must stay full and drainage must not overflow the sump.

Second Principle: The aquarium must not overflow if the siphoning apparatus has a problem.

Third Principle: The system must continue unaffected after a power outage.

These three principles are achievable and the floor can stay completely dry!

Holes drilled in small tanks can cause cracks and leaks because the glass is so thin.

In this alternative to drilling the glass a siphon pulls water over the aquarium top edge and into a box. There is a standpipe in the box which allows water to flow out only when it rises above the top of the standpipe. Here is a drawing that was done for me. It’s not totally accurate and not to scale but gives the general idea. And it’s better than the drawing I once used!

(The siphon and standpipe tubes should be at least 1” diameter; 1¼” or 1½” are preferable. Also, the water level in the overflow box will always sit at the top of the standpipe not submerge the standpipe.)

It's self regulating. The higher the water in the aquarium, the faster it goes down the pipe. The blue line shows the water level in the aquarium on the left and in the siphon box on the right. The siphon box is a "Lee's" specimen box like the LFS use to place fish in after netting before bagging. It hangs on the outside of the aquarium. It has a PVC pipe running through the center.

Cut a hole the size of the PVC pipe in the bottom of the box. Class 200 PVC has a larger I.D. allowing more water through and 3/4 inch pipe has never been large enough even for small tanks. The box is made of fairly brittle plastic so be careful. Don't worry, if the bottom splits while drilling. A fracture can easily be patched with "aquarium silicone" found in squeeze tubes at Home Depot. I didn't have a hole saw attachment for my drill so I drilled a lot of small holes in a circle and used a file to smooth it down to fit the pipe.

Cut a 1½” inch length of pipe and get two couplings. Glue the stubby piece of pipe halfway into one coupling and then push the other end of the stub through the hole in the box. Use a lot of PVC cement when you put the coupling on the other end of the pipe and press the couplings together squeezing the bottom of the box between the two couplings. If you want to be extra sure it won't leak, after the cement cures(12 hours), put a bead of silicone around the joint on the inside of the box. On occasion I have had to shorten the coupling because of the particular tank or desired water level in the aquarium, so it's good, before glueing it together, to set the coupling in the box and hang it on the side of the aquarium, checking to be sure there is at least ½” between the desired aquarium water level and the top of the coupling in the box.

A length of PVC glued into the bottom of the lower coupling allows you to place a flexible tube over the end which will take the water down to the sump. I found a white

flexible corrugated plastic pipe called bilge tubing works really well. It can be found at Lowes and boat stores and was once available at Home Depot. Silicone the connection to prevent salt creep.

The coupling inside the box needs a piece of pipe cut to just the right length to keep the aquarium water at the desired level. Do not glue this pipe in place because you may need to try shorter or longer pieces. Glue is actually unnecessary for this piece, because the fit is tight enough that over time a little biofilm growth effectively seals it. Depending on the size of pump in the sump, the water in the aquarium will stay about ¼” above the level of this pipe.

The siphon is simple if you buy one or two(recommended) "U" tubes at the LFS. The bottom of the siphon tube inside the box must be lower than the top of the standpipe, otherwise the siphon cannot work because the end is not submerged. The easy way to start the siphon is to suck the air out through vinyl tubing installed in the "U" tube.

Drill a small hole at the top of the inverted "U" and silicon an airline on top. If you use air tubing you can run the other end of the tubing to the venturi air input of a power head in the tank (as described on the website about the weir). This will keep air removed from the "U" tube. The other method is to put a real good plug in the end of a foot or more of tubing, and when the "U" gets a big air bubble, hold the end of the tubing up in the air, remove the plug, wait a moment for the water to clear out of the tubing and when ready, suck the air out of the "U" tube to restart the siphon.

The best way I’ve found to put the air tubing into the top of the "U" tube is to silicone one end of those small black sprinkler drip tubing "L" couplings into the "U" and when it's cured push the air tubing over the other end. A big gobb of silicone is a good safety measure! These "L"s have a little flange so you can drill a slightly smaller hole and push the flange through, then pull it back to the flange and gobb the silicone around it. That way the opening is right up close to the highest point in the "U" and all the air bubble can be sucked out.

Inside the aquarium there are two options. 1) make a skimmer box that the "U" tubes go into, or my choice, 2) place a strainer over the end of the "U" tubes. I actually extend the tubes down to the bottom of the tank so that circulation is taking bottom water and some detritus is removed too. This may help aeration too since deeper water is less oxygenated. As it ripples down the corrugated bilge tubing the water gets oxygenated. It's also a good place for lots of nitrifying bacteria!

A nice looking siphon can be made with black 1 ¼” ABS pipe with black ABS fittings. Black is less noticeable than white and it coats with coralline algae a little faster. One pipe at 1 ¼” draws approximately the same amount of water as two one inch pipes. ABS pipe sometimes floats so make it long enough to stick into the sand to hold it down. It will waterlog after about two months. A rock leaning against it could also keep it from floating up. For a strainer on that large pipe, I bought black needlepoint “plastic canvas”. It's a plastic screen material that is good for many screening uses in the aquarium. Cut the bottom end of the ABS siphon tube at an angle facing out and cemented, with ABS or silicone, a piece cut just the right size to fit over the oblong opening!

For a DIY project this looked pretty good. I once had two siphon boxes, one on each back corner of my 75 gal reef. The boxes are fairly hidden and the black pipe in each corner does not seem to detract from the tanks beauty. It also takes up less space than the All Glass Aquarium brand with their curved black plastic piece in the corner. If you look at that design and how those tanks work, you will see that the principle is the same as this siphon box.

The pump in the sump that is best is a powerhead placed close to the surface of the water. If the pump is placed down on the bottom of the sump and the siphon box stops working because of air in the "U" tubes, the pump will empty the sump and usually cause the main aquarium to overflow. It's okay to have the Pump sucking air. It won't ruin it because enough water remains around the impeller and housing to keep it from burning up. The water lines up into the aquarium need to be either partly out of the water or a small branching portion needs to be out of the water.

Supply lines can siphon too much tank water back to the sump. To prevent this, drill a small hole in the supply lines at water level, but this can lead to disaster if a snail covers the hole just at the wrong time or algae is left to clog it. Be aware that a sump needs to have enough capacity to handle the water that flows down from the aquarium when the pump stops. A good rule of thumb is a half full sump.

Some sumps are simple plastic storage containers, but using glass or acrylic aquariums have the advantage of being able to view all the critters. An RDP refugium is closed up to keep the light from shining out at night and keeping it dark in the day. There are dark heavy fabrics that work well to cover the back of the stand, allow pipes and wires through and allow the sump area to "breathe".

Evaporation draws down the level in the sump only, not the main aquarium. A lot of air blown into the aquarium can quickly fill the "U" tubes with bubbles so be careful to keep the siphon going.