Corals looks bad, no reason!

Hi..

I have been reading a lot on this forum.. learning ... learning..

I have been working in my reef tanks for 6 month... all looks perfect... the only problem that I have so far.. are the diatoms alge..

So I add phosguard and reactor..

When I did that.. I also changed Toadstool Mushroom Leather Coral from location... the flow was too high and the base of the Mushroom breaked off.

So I look the coral in bad condition.. like dying..but I leave in the thank

In addition I performed test my Mg parameters and was in 1200pp...

So I raise to 1320... 120 in only one shot..

The next day my corals looks bad.. zoas only onpen at 50%.. and then the other corals one by one... followed the same path..

I add carbon and purgin in order to eliminate the possible toxin of the Toadstool ME....

But I dont know what really happen...

Was the addition of the Mg was fast?? or the toxin of the Toad Mushroom? or what?? that was..

All my water reading looks good... my water are from R/D.. are good water..

Please your advise..