Alkalinity Burn or something else?

[NuraNori]

I pour the alk buffer in the left compartment of the sump (where the water from the DT comes in), so then it has to go over some baffles into the return compartment. I mix the alk with about 2-3 cups of RO water and put it in about 5 sloshes over 30 min.

Oh and we've been dosing alk for about a month. We were suspicious that it was alk burn so we changed from Kent Part B to Reef builder because we thought it would keep the pH more constant.