Total Pageviews

Monday, September 5, 2011

5 - Connecting the Fish Tank and Sump

Piping connecting the fish tank to the sump

It’s not always true that water flows downhill.

What is true is “fluid will flow from higher pressure to lower pressure.” In order to achieve this equilibrium, water will do some pretty whacky things. What we want to do is connect the fish tank and the sump such that:
  • Water in the fish tank will never siphon out completely
  • Water from the bottom of the fish tank will leave the tank, carrying away solids
  • No openings are large enough to ‘suck’ small fish out of the fish tank
  • My ‘sump’ can rest on the same surface as my fish tank

Tall order! But it can be done. I want to acknowledge up front that I didn’t invent this design from scratch. It is a modification of the “Constant Height of Pond” or CHOP systems originally popularized by Murray Hallam, as so beautifully explained in this post by ecofilms: CHOP and CHOP2. My ‘addition’ is translating this into standard pipe sizes that can be found in the US. The 365 Aquaponics design is partway between CHOP and CHOP2 - like a CHOP1.5.

The drain out of the fish tank must be higher than the drain into the sump. If the sump is higher than the fish tank, you’ll never persuade the water to leave the fish tank. But the piping between the fish tank and the sump can bend or run under the ground if needed so the gardener can walk freely between the tanks. The three sketches below are “equivalent,” as far as successfully draining water from the fish tank to the sump.

Water will flow from high pressure to low pressure

But it isn’t enough to just connect the drain from the fish tank to the drain into the sump. I want to pull water from the bottom of the fish tank, where all the nutrient-rich sediment collects. So I’ll put some simple pipes into my fish tank to pull water from the bottom, as seen in this picture of my prototype:

The fish tank, with pipes to suck water up from the bottom

One minor issue with using the standard, inexpensive, pipe sizes is that sometimes the water level in the fish tank rises faster than the water can escape through just the lower parts of the two pipes. In that case, I allow water to escape through the top of the pipes into the drain. Below is a video clip of me drilling the holes in the fish tank and sump and installing the bulkheads.


  1. To avoid "rip-outs" when using spade/paddle drill bits, drill half way through from one side, then drill from the other side using the 'pilot hole' created by the drill bit to finish the hole.

    The spade drill bits with 'spikes' or teeth on the outside edge that cut the outline of the hole before the body of the drill bit removes the majority of the material are much better than cheaper bits that don't have teeth.

    Same thing if you are using a hole saw - cut half way through from one side and then finish by drilling through from the opposite side.

    1. Another tip I came across when making a 5-gallon swirl filter is to use hole saws that have lots of little teeth. The inexpensive hole saws with only a couple of teeth are designed for wood - on a curved plastic surface, the cheap hole saws have a high likelihood of ripping big jagged holes in the plastic. So sad!

      Since I see this post is one of the posts frequently visited by folks who came direct from a search engine, let me mention I ended up getting tapped to write The Complete Idiot's Guide to Aquaponic Gardening for Penguin Book Group. The book is now available for purchase at It includes lots of DIY plans as well as everything I wished I could have found in a book back when I was starting out (which wasn't very long ago...). So far the reviews are good!

  2. Another trick I'll do sometimes is put a board behind the thing I'm drilling. That works great if you're drilling something really thin, like a water bottle.

  3. What is the configuration of pipes in the fish tank?

  4. I have 1-1/2" bits of 3/4" pipe connecting the inside portion of each bulkhead fitting with a 3/4" SSS T. I then put a long 3/4" length of pipe into the bottom part of each T that reaches almost to the bottom of the tank. That way the tank drains preferentially from the bottom (where all the waste tends to settle).

    If I were doing this from scratch, I'd probably use 1 inch pipe. I'd also use 2 inch net pots connected with zip ties to create strainer baskets to keep fishies from getting sucked up (or down) into the piping.

  5. Thank you so much. I LOVED your presentation at the conference and I am copying your system with just a little change (a bigger tank). I just didn't look closely enough to see how you connected the tanks! Thanks again!

  6. Thanks for the info on your blog. You really helped me out a lot. I'm planning to do a water test tomorrow to see how everything is working. Nice idea with the garden hose diverter system. I found a drinking water hose at Home Depot called "NeverKinK". There are other versions there that aren't safe but this one stated that it was safe.