Yes if you are leaving your return pump on while doing water changes, your water level in the return section of the sump will lower because the total system volume is lower. This is how the ATO works through gravity. Set up your sump so the water level when full is just above the float closed height (since you can't raise or lower the stock red sea float much). I just grabbed the float and lifted it lightly until i felt resistance and made a mental note of the float height compared to the bracket it is attached to. This is your ATO float closed height. So as I was saying, set up your sump so the water level in the return when all pumps are on and equipment are in the tank so that the water is jus above the float closed height. Then fill your ATO and open the ATO float valve and leave it for a week. Don't make changes to the overflow/return flow height in the DT weir because those changes will either drastically raise the return pump section water level or drastically lower it. Then confirm after a week your salinity is the same (as long as you kept the ATO resevoir topped off the whole time). And like I said previously, if you are fiddling with your overflow valve to get the trickle to quiet down, close the ato float valve before doing it.No, I haven’t urned it off. Honestly didn’t think I needed to if I was only pulling water from the display tank. The Red Sea reefer comes with instructions on how to put it together but not how to do proper water changes! I even tried watching YouTube videos on how to do water changes with a sump and ATO! Lol this is my first all-in-one tank so still getting the hang of this.
I feel like an idiot, that’s probably exactly what the issue is Lol! Thank you