Sump issues

sumpreef · Mar 29, 2026

Hi all,

We are new to saltwater. Long time freshwater fish keepers and are on our new 40gallon breeder with a 20gallon sump below. However, we seem to have issues with regulating outflow and inflow and would appreciate any guidance. We can't seem to get the flow quite right. Right now the return pump is set at 40% (

Jecod/Jebao DCT Marine Controllable Water Pump (DCT-4000, 1056GPH))

The outflow to the sump is compreised of two drains. One main drain with a valve that regulates the flow and another emergency drain that is wide open incase the water level rises in the overflow box..

This is tempered glass so I can't drill it. I have the eshopps PF1200. I realize it is a little big for this system but I have removed one of the black u tubes to reduce flow.

A couple of assumptions I have made and please correct me if I have many incorrect ones.

1. The tank level height is set by the black skimmer box and water evaporation manifests only at the return pump section of the sump.

I'm testing with freshwater now to see how the system works. I simulated a water change by turning of the pump waiting 2mins and then turning it back on without taking or adding water and the water level in the return section of the sump is different that what I started with . This is what I am perplexed with

Any advice or tips would be greatly appreciated. I have attached a couple of pics to help

Shirak · Mar 29, 2026

Water level looks the same to me so not sure what you mean on the return section different. Sometimes takes a few minutes for things to adjust after turning the main pump back on if air is stuck in the main drain line initially. Key thing is the sump holding all the water that drains from the display if the return pump is off for a bit.

You are correct that the level in the tank is set by the overflow in the tank. You are also correct that the level in the section where the return pump is will drop from evaporation before the other section.

Sounds like you have the return pump set at a pretty good rate for the size of the tank. Usually looking for around 5x or maybe a bit higher tank volume turn over through the sump per hour. Also look like you have the flow valve on the main drain pretty well dialed in so you have a full siphon and not sucking air down to the sump.

sumpreef · Mar 29, 2026

Ok thank you. I played around with it more. I started using the valve from the main drain as a coarse adjustment and played with the motor power to fine tune the rate at which water empties. Looks like water only drains as fast as the pump pumps it back. Thanks for your help!

1ocean · Mar 29, 2026

not a fan of those over flow tubes that go over the tank top...They get air trapped over time and slow down the water flow...I remember the headaches when this was the only option with fresh water tanks in the 1990's...
best to keep you eye on this each day... If the sump loses water height then the pumps will run dry...

TokenReefer · Mar 29, 2026

If yiu put a smaller length pipe in the other downpipe opposite of the emergency drain in the external box so that the water level stays above the u pipe ouket it should never break siphon eve when pump shuts off and yiu can dial down or up