Sump Size?

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Aquarium Advice Freak
Jun 11, 2017
SE Kansas
I've been thinking about getting a sump for a few tanks. I'll DIY them, but I need to know how big of one I need. All tanks will have a DIY lily pipe spin outflow.

The first is for a 90g Angelfish tank. Either 6 juveniles, or a breeding pair of adults. A school of a dozen or two Bleeding Hearts, four BN plecos, and the Time-Out for Venezuela Rams that need it. It'll be heavily planted.

The second sump is for a 55g Apistogramma Biotope tank. The stock will be a breeding pair of Apistogramma A school of Glowlights at least a dozen strong, a few BN plecos, and a pair of Venezuala Rams. It might be planted, or I might not.

The last will be for a 55g Axolotl tank, which will have an egg crate lid with Pothos growing out of it and into the water.
The DYI sump that came with my 90 G tank is 20 gallons.

I have a 40 G long tank for my two axies. And an egg crate lid. HOB & large sponge filter. I have a plastic guard below the filter that limits water splash into the tank.
I used a custom 25 breeder tank as my sump for my 75 gallon tank. It was 30" x 18" but only 10" tall. So you really need to figure the height of the sump as much as the gallonage and what you intend on doing inside the sump. The more things you plan on doing inside the sump, the larger it should be. Other things to consider: are you going with an inline return pump requiring holes in the sump or are you going with an internal pump that sits inside the sump. What size plumbing are you using. The larger the diameter of the plumbing, the more water that will be inside the pipes so that needs to be compensated for.
So there is a lot to consider when adding a sump before you can answer " How big?".
I like sumps to be about half the size (or bigger) of the main tank. This means you have plenty of room for the extra water that drains out of the main tank when the pump is turned off. If the sump is too small, the sump can overflow when the pump is off.

Small sumps also need topping up more often and there is more chance of the pump running out of water or not having enough water to run properly.

You need to work out how much water is going to drain out of the display tank when the pump is off. If 50 litres of water drains out of the display tank when the pump is off, then the sump needs to be able to hold that amount of water in addition to the water that is normally in the sump.
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