sudden fish death

[S2minute]

Folks, i have a problem. I have a large multi-tank system. I feed it cultured phyto and i've been doing it for some time. One of the connected tanks is cryptic/semi-cryptic and has alot of natural sponge growth. I have been fighting a bryopsis outbreak most likely because of the phyto.
I have a mixed coral tank with sps/lps and a few zoids. I also had alot of fish all of which have been in the system for a long time. Two things i do know due to a recent temp spike of nearly 10F i lost several sps corals. I found out what happened and corrected. My PO4 with Hanna converts to .07 which i'm not happy with. My Mg test kit was giving my false readings so when i bought another it read 1735. Since, i did 2 water changes and stopped supping Mg. Now i'm at 1590.
Yesterday, before i had to leave for work, my blue/green chromis suddenly started dying. I read that they do that out of the blue. Then before my eyes one of my Benigni Cardinals got progressively weak and died. I had to leave for work, there was nothing i could do. When i got home after 16 hours, the other was missing, my algae blenny , powder brown dead. My six line is mia as well as an anthesis. Only thin i can see left is my big sailfin tang, an angel and a clown and some damsels.
I changed the carbon and added some trace elements...there was no apparent signs of the cause of death of the bodies. I have not added anything new to the system except some sps/lps frags i bought at a swap a couple of weeks ago. Any ideas??? Thanks

 

[Cloudburst2000]

Were the fish gasping for breath? Possibly an O2 problem?

 

[irishindoexpat]

When was the last time you did maintenance on the tank? and what equipment did you use like buckets etc for it that could have been used on other chores around the house ?

 

[S2minute]

sudden fish death

Were the fish gasping for breath? Possibly an O2 problem?

The chromis deff exhibited rapid gill movement and darted all over the tank before death. The others did not. It's as if they died in a shot time w/o the rapid gill movement. It's as if they just got weaker and weaker then died. I have about half my fish left which seem to have been unaffected.

Everything equipment wise was the same as usual for maintance. The snails,crabs and other inverts are unaffected. I have a large ETSS downdraft skimmer which really puts O2 in the water and there is good Surface Agitation in the sump and DT surface. However it does sound like a temporary O2 problem. Maybe it was a bac bloom as as result of a phyto feeding??

 

[SushiGirl]

Bacteria blooms definitely deplete oxygen.

 

[avangeline]

Bacteria blooms definitely deplete oxygen.