High alkalinity, low ph?

[marcos77]

hi, I just tested my ph and it's about 7.8 - 7.9 and my alkalinity is 13.3 dkh or 4.75 mequ/l. I thought that high alkalinity would prevent ph from dropping? I have a 18G that is about 3 months old. I only have one damsel fish at the time and about 18 pounds of live rock. How can my ph be low if my alk. is high? Last night I did a 10% water change. I also want to mention that I add about 2 1/2 cups of distalled water directly to my tank every day to replace from evaporation. I do know that distalled water has no kh, could this be the problem and if so, what should I be adding to the distalled water? thanks

[tendar]

RO water is better or RO/DI water is best used.
I never was very good at remembering ups and downs on ph and alk and how they react to each other. The Alk should come down on its own though.

[DyeLooper]

Try Osmo-Prep by kent marine, will raise the ph of your Distilled or DI/RO water. Distilled if like RO/DI also has low Ph. Osmo-Prep will raise the Ph but also has alot of dKh also.