Alkalinity swings with Hanna checker

[boxgj]

I noticed on Sunday night my alk is at 8.9 and this morning Thursday 6/19/25 my alk is 9.4. I have about 11 sps frags in the tank. I thought I would have to start dosing kalk and all for reef but I was wondering could it be a margin error with the Hanna checker?
I tested the alk twice Sunday night and got that same reading of 8.9
But I also notice a few of my acro frags are encrusting on the rock and growing a bit

 

[bubbgee]

I found Hanna alk, cal and mag temperamental in their test kits. I switched to Salifert and I was more comfortable with the consistency.

I only use Hanna now for the nitrates and phosphates.

 

[Randy Holmes-Farley Verified Community Expert]

I noticed on Sunday night my alk is at 8.9 and this morning Thursday 6/19/25 my alk is 9.4. I have about 11 sps frags in the tank. I thought I would have to start dosing kalk and all for reef but I was wondering could it be a margin error with the Hanna checker?
I tested the alk twice Sunday night and got that same reading of 8.9
But I also notice a few of my acro frags are encrusting on the rock and growing a bit

If you added no alk in that time in any way, including water change, then it is test error.