RO/DI and Alkalinity

[LedZeppelinfan101]

Here in Lafayette, our water is ok, but not great. At the store where I work we were using all RO/DI water, but were having trouble maintaining a decent alkalinity in the reef tanks. We switched to tap water treated with Amquel to get rid of chlorine/chloramines/etc. and now the alk is back at a more than reasonable level. Anyone else had similar problems with using only RO?

[grallster]

Yes--fresh RO/DI has a high level of carbon dioxide which when dissolved forms carbonic acid. When you add the salt mix the pH come out alright because all the buffer gets sucked up by the carbonic acid. Try aerating the water for an hour before adding the salt. You could mix up some sodium bicarbonate in the water first too I suppose.

[bklynmet]

very good points Dave.

[grallster]

Of course if you mix your RO/DI top-off with kalk you've got nothing to worry about.