Water Change & Top Offs

Brandon Johns · Mar 21, 2019

I just purchased an AUTO AQUA AWC/ATO for my tank, curious if I would have to even top off my tank with fresh RO/DI water if the AWC is doing 2% water changes daily. Wouldn't it keep a consistent salinity? I have a 20 gallon reef tank and the evaporation is pretty much non existent. I top off with fresh RO/DI water as of right now because I do a 25% water change weekly and even then the evaporation isn't very much. Maybe just play with the AWC/ATO and see what happens? Any opinions are appreciated!

Thanks,
BJ

Hitman · Mar 22, 2019

Just keep a eye on your salinity as time goes on without topping off with rodi your salinity could go up.

stacksoner · Mar 22, 2019

Brandon Johns said:
I just purchased an AUTO AQUA AWC/ATO for my tank, curious if I would have to even top off my tank with fresh RO/DI water if the AWC is doing 2% water changes daily. Wouldn't it keep a consistent salinity? I have a 20 gallon reef tank and the evaporation is pretty much non existent. I top off with fresh RO/DI water as of right now because I do a 25% water change weekly and even then the evaporation isn't very much. Maybe just play with the AWC/ATO and see what happens? Any opinions are appreciated!

Thanks,
BJ

Seems like you answered your own question there.

Brandon Johns · Mar 22, 2019

slewrock1 said:
Seems like you answered your own question there.

HAHA kind of, right.. Maybe someone has some experience with this thing that could chime in with their routine.. Don't want to kill off any of my livestock.

Tastee · Mar 22, 2019

Any evaporation needs to be topped up with RODI. Water evaporates, salt does not. If you just keep adding SW your salinity will rise. Theoretically you could calculate your evaporation rate and top up with SW at an equivalently reduced salinity but I would never do that. Your evaporation rate will vary with environmental conditions making this a lottery.

You will however lose salt gradually due to creep and skimmate, so that needs to be replaced. Standard setup is ATO to replace evap, AWC replacing exactly what it takes out and occasional extra salt in the ATO to accomodate losses due to creep, skimmer etc.