High pH is a fairly uncommon problem in reefs in my experience. I would verify your test method a couple different ways before going nuts with adding anything to lower it. pH varies over the course of the day and if you top out at 8.4-8.5, I think you are just fine.
If you finally decide it needs to be lowered, although you can use vinegar, carbonated water would be a better bet. That way you are not adding a separate carbon source that could be a source for problems in a couple weeks.
I will re-test the PH and it was about 10 in the morning I tested. I'm scheduled for a 15% water change and I will test again after. My Alk is about 7 dkh and with the PH on the higher end, will that cause any problems? Can I adjust both in one method?
It has normally been about 8.1-8.2 but it has tested this high for a little over a week. After the first test a little over a week ago, I did a 15-20% water change. Very little kalk was adding during that period as well. Nothing out of the ordinary.
Maybe it's my test kit. I am using a Red Sea test kit for the PH and Alk.
Sorry I didn't notice your reply back before now... I think 10 is an erroneous result. Unless you're adding something to raise pH, I can't see it ever getting that high on it's own. Not to mention I would guess that many creatures would start to perish with a pH that high.
Before you do any adjusting, you need to get another test from a different kit or method.
(BTW - I merged your new thread with this older thread and moved it to beakerbob's chemistry forum.)
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