Alkalinity dropping fast

[JGoo]

Hi everyone-I am at a loss at this point. I have a 25 gallon fusion lagoon, it has been up for almost 2 years now. I had a major tank crash after a power outage a year ago. To make a long story short I lost most of my corals except 6 LPS. After that dinos took over which I almost have defeated at this point. So to the point. I always dosed 2 part for calcium and alk. I made a switch two weeks ago to kalk dosed threw my tunze ato. I raised my parameters using two part and started the Kalk. So I had my alk at 7.3 and it drops the next day to 5.2 at the same time the next day. My calcium does not drop as much but will drop 30ppm in a given day. Mag at 1320. I am not sure why there is such a major drop in parameters each day. especially when I have so few LPS corals. I have been in this hobby for 11 years and have never had such swings. Any advice would be much appreciated.

dkh test-hanna
calcium-Red Sea
Mag-salefert

Thanks

 

[JGoo]

Not even sure that this type of swing is possible and could it be a problem with my hanna dkh checker. I used new regents with the same 5.2 dkh result. Could evaporation rate be an issue? Could low magnesium cause precipitation of alkalinity and calcium? Possible problem with my magnesium test kit?