Alkalinity Problems

[Jarrito]

Hi everyone, I've had this tank running for about 3 months and currently have only a pair of clowns. I just ordered some coral that are arriving next Friday. Recently I have been testing for Alk, Ph, and Ca. Ph stays around 8.2 and Ca is above 500 but then my Alk seems to be dropping and I don't know why. It went from 8-6 in a little less than a week. Do I need to start dosing Alk? and how would I get started? What could be consuming it?
Nitrates are at 0 as I heard increase in nitrates can decrease alk so it can't be that.

 

[gbroadbridge]

I would double check that your salinity has not dropped.

 

[Jarrito]

Currently at 1.025 but I just topped it off a couple days ago when it was around 1.026

 

[Townes_Van_Camp]

Salinity drop or testing error. If you haven't didnt do a water change before the ALK drop occurred, my money would be on a testing error.