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[Jdale78]

Hello. How far below desired water level should my ATO sensor be? Before it is triggered to add water.

 

[JTP424]

Depends a BIT on the ATO itself, you want it low enough so it doesn't hit the "overflow" limit if your ATO has one, but you don't want it SO low it runs dry....
What ATO do you have???

 

[JumboShrimp]

Great question. In general I would say, 'How much fluctuation in salinity are you willing to tolerate?' I have a 150-gallon FOWLR and "no" ATO, and my salinity can drop quite a bit over time before I stop being lazy and top-off. Even with a reef tank, I would think much would depend on the sensitivity of your corals (hardy/cheap corals v. expensive/sensitive corals). You can try your ATO at different levels and test how your salinity changes at each 'step down' or 'step up', and see what level you prefer as a salinity swing. My 2-cents, anyway. I hope this helps.

 

[get-salty]

Normally, you would put the ATO sensor in the Return chamber.

The water level in the return chamber should be above the return pump ~4-5" (at least in my sump) when pump is ON.

And this is where you place the sensor - at that 4-5"
Very important to place the ATO sensor where water is calm so that it wouldnt get triggered.