What killed my fish?

[Bill King]

I did a water change yesterday, & something very fast acting killed some, but not all of my fish.

That's the short version. Now some background.
75 gal running for several years. Bare bottom, lightly skimmed,LPS & leathers mostly, very light fish load.

Several weeks ago I had a "brown jelly" event on a huge frogspawn. I started charcoal, & removed all of the affected heads I could find. I thought the whole tank would die.
Recovery was good, & nothing else was affected, except for an algae growth which I figured was due to some of the die off.
Yesterday, I finally did a large water change, along with a lot of algae clean-up, and removal of the rest of the "dead" deads of the frogspawn.
I notice some distress in the fish while all this was going on but figured I was just stressing them out. Within a couple of hours, two clowns and a damsel were dead. I've had these fish for years! If that wasn't strange enough, a spotted hawk and a yellow watchman goby are healthy & active today?
All of the inverts are fine, in fact the serpent stars had a feast last night, all the corals are fine?
Did I release something that was "tied up" in the algae or dead coral?
Did the fish try to eat some of the nasty stuff swirling around?

I don't want to restock if something is deadly in the tank.
thanks for any ideas.

 

[raynist]

Was this a new bucket of salt for the water change?

 

[acer]

yep - bad salt was the first thought I had also. Did you check the PH, etc. before adding it?

 

[Bill King]

I thought of that, I had used from this bucket before. It had drawn some moisture from being opened, hard salt around the edges, but everything else was just as I've been doing for 20 years.

Thanks guys

 

[ironwill723]

Sounds like you stirred up/released some type of built up toxin in your tank during the water change IMO. (unless your salt was bad) If it was me I would replace and run more carbon and make sure there are no dead flow areas in the tank where bad stuff can accumulate and see what happens with current inhabitants. The recent water change probably did improved your overall water quality from before the deaths (again as long as salt mix wasn't bad) but you might want to do another partial change in a week or so with a different salt mix or new batch just to be sure. Maybe test water parameters over next few weeks as well. That is what I would do anyways.

 

[acer]

Also - do you run a sump/refugium? If you took the water out of that area - then put water back in it would probably stir up a lot of stuff on the bottom of the sump/refugium which may have been where the toxins had accumulated form the coral problem a few weeks earlier.. I did this a month ago in my office tank setup ( being in a hurry - of coarse) and got a Cyano bloom within a day from the detritus, etc. that I have not yet gotten rid of. So just to be sure the PH/temp,etc. of the new batch of water was the same as the tank water you took out? And the new water was mixed for several days prior to it being added? Also how "large" of a change =50% ? Maybe the new water was just too much change for the free swimming fish that were swimming right thru it immediately and the fish that are not free swimmers (that have a slower metabolisms and would get a more gladual water change toward the bottom of the tank) could handle the gradual changes easier. Just a few ideas.

 

[bnmir]

Seem strange to anyone else that the bottom dwellers, (goby, hawk) survived while the clowns and damsels died?
All are pretty hardy species.
And the inverts are fine, which are typically more sensitive to anything chemical.

 

[ironwill723]

Also could of been RO/DI water if used immediately in the salt mix. If not well circulated after mixing the water will have little dissolved oxygen in it from going through the RO unit. Perhaps suffocated the fish swimming near the top?

 

[Reefbox]

What r your water change details?

Was it aerated and mixed well? For how long?

What is your chlorine/chloramine removal process from the tap source?

 

[livingcorals]

Something in the water might have caused a spike to occur with the water.

 

[Bill King]

Thanks for all the ideas guys.

I'm really leaning toward a DO sag. I don't have the heat on in the fish room yet, so I threw a heater into the salt-mix bucket to warm it up a bit. I'm thinking the warm water (maybe too warm) equaled a very low DO when I started adding the new water.

My routine has never changed.Start with fresh RO water aerate & stir with a power head for a day, add salt mix & continue aerating for another day.
I always turn off the return pump, & siphon from the display.

I've been in this hobby for 30 years & I'm still learning.

Anyway, the tank looks great, minus a couple fish, which I always regret.
Thanks PMAS
Bill