Sump return chamber size important for salinity?

Trever · Mar 24, 2021

While making my own sump currently, I'm trying to think about my experience with my existing sump/DT. It seems to me the smaller the return chamber, the easier it is to detect evaporation and correct for it (manually or with ATO), thus maintaining a very stable salinity.

But I love the idea of one big open chamber after the filter sock drop chamber (heaters will go in drain crash chamber just before the filter sock drop). Among other things it gives me lot's of options over time. Can just have a big huge 8" water level chamber where the return pump is down on the far end.

It's only a 15 gallon sump. But it is also only a 20 gallon long DT, so not a system with a lot of water.

Which consideration should win out here? Put a baffle before the pump (thus creating a smaller return chamber but sorta losing 4" of precious sump space)? Or have an open concept? Very interested in thoughts/experiences.

At least for the first year or so, this will just be a FOWLR, if that matters.

schuby · Mar 24, 2021

A few things to consider:

If you put in a baffle and create a return section, then the water in that section must be enough such that it doesn't go dry when you turn your return pump back on (after being off). It takes a few seconds for the flow to get back to your sump and then back to the return section. If the amount of water is too small, then the return pump will start sucking air and it will be rough getting the flow going again, at first.
If you keep the sump as one, big section and you run a skimmer in it, then the micro-bubbles from the skimmer may get to your return pump and then to your DT. A return-section baffle helps alot with skimmer micro-bubbles.

Other than those two things, a wide-open sump works fine to maintain salinity. On my first tank, 90 gallons, I had a ten gallon sump. I literally drew lines on the sump with a marker for where the water line is when the pump is on and where the water line is with the pump off. This allowed me to manually top-off the tank to the proper water level. The levels varied some as the pump got gummed up, but it was sufficient.

In my current tank (150 gallon DT with 40 gallon sump), I have an ATO and AWC. It is so much nicer and stable!

ca1ore · Mar 24, 2021

You are correct in that a smaller return chamber means the ATO will trigger more frequently and add less water each time. That will maintain a more stable salinity, though the variations would still be quite small even with a larger return chamber. Easy enough to configure the baffles so that the pump does not run dry on start up even with a small return chamber.