evaporating water in new tank. Topoff?


New member
My tank has been up and running for a week now. Just 40lbs live sand in there with a heater and my emperor 400 filter. The filter has gotten quite loud due to water evaporation. I wanna throw some more water in there. My question is the water i add in do i mix salt in with it or not? Thought i read somewhere that when water evaporates the salt stays in the tank. And if you mix salt in new water your salinity will go up.


New member
Top off with fresh water, salt stay behind from evaporation

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New member
Evaporated water is lost fresh water, top off with fresh water/no salt

Water changes you are taking salt out , then add new salt water in at the same salinity
The same volume of water taken out should equal the same volume of water added at the same salinity


New member
+1 Yes, replace evaporated water with frest water. Two points for research and consideration, if you haven't yet. Both of these are money well spent, IMO.

ATO - for automatic top off.
RO/DI - for water purification.


New member
probably want to try and top it off more often than a week as well, probably daily to 2x a day depending on how much you lose, or use an ATO.


New member
Once you actually have any sort of livestock in the tank, you will definitely want to monitor your evaporation and salinity more closely. If you lost enough water to make the filter splashing loud, your salinity probably went up quite a bit. Swings in salinity like this are not good for any livestock (including beneficial bacteria)

gone fishin

New member
what everyone else said. I have a sharpie mark on my sump for the normal water level and another mark for the daily evaporation. If the level is way off from the evap mark time to look around for a problem.