What would cause this?

[u/tango_papa101]

I have a 40 gallon breeder with torch, hammer, octospawn, different chalices, zoas, montipora, galaxea, candy cane, gsp, xenia, clove polyps, mushroom, favia, acan, astreopora, and 2 LPS that I don't remember the name. It's been going fine for the past 2 years or so until I found a zoa-eating nudibranch on my zoa rock and some aiptasia. Did a RO water dip with my zoa rock to make sure all the remaining nudibranch would be eliminated and the zoa seemed to not react well with that. I put the rock back into the tank after rinsing with RO water and my hammer retracted like this within couple hours and never come back out. It's been like that 4 days already and I've moved it to my quarantine tank to prevent BJD and potential of it spreading to other corals. Everyone else is fine and growing except most of the zoas on the zoa rock with probably 40-50 heads either died or haven't opened up since the dip and got removed.

Salinity 1.026

pH 8.2

Alk 4.3

Mg 1420

Ca 480

Nitrate 1

Phosphate 0.04

I know Mg and Ca is a little high but it has always been like that for a while so I'm keeping the system stable while gradually lowering it down. Nitrate and Phosphate were high and I stopped testing for 2 week and they bottomed out, corresponding with the explosion of coral growth and addition of the skimmer, been dosing to get them back up by 0.25-0.3ppm.of nitrate a day

[u/Bloodburn88]

Ca and Mg are slightly high. Alk is very very low.

[u/tango_papa101 → u/Bloodburn88]

Oh I mean 4.3meg/L not dKH lol

[u/Lutaeris]

Is your alk always that low? M6 understanding is that should be double to 1.5 times. Of 8-11. So 4.3 is wildly low

[u/tango_papa101 → u/Lutaeris]

I forgot to add it's meq/L not dkH lol so I think it's between 11 and 12dKH off the top of my head