Unknown Toxin

[azzala]

I have a 70 gal tank with a wet dry filter, protein skimmer,LS, shells and coral for decoration. It has been running for over 4 months with the following reading:
Nitrite - 0, Nitrate - 5, PH 8.0, Alk 1.7, (rechecked by lfs) Temp 78. I had a powder tang, a damsel, a pajama fish and a maroon clown. They all died in one day except the clown which is recovering in the Qtank. The cleaner crew of snail and hermits are doing fine. No copper was added and no chemicals sprayed on or near the tank.
Here is the big question. A toxin got in from somewhere, what will it take to start over safely?

 

[fixitdude2001]

If I am reading right you put all these fish in all at once? This is typically a big NO-NO, as the tank is not ready for that much of a load all at once, You didnt mention ammonia leval? with this many fish at once you can have a high spike, wich will kill most fish. cya

 

[azzala]

No the fish were added gradually. I had one from a previous tank that went in first and then I added the rest about one a month. The amonia level is 0. Like I said I had all the test redone by the lfs and they said it all checked out fine. Somehow, a net placed on the floor, a cleaner used in the next room...the lfs asked if I used room spray which I don't...somthing killed them. I want to know how to make it safe again.

 

[kappadoku]

PH is to low. Not low enough to kill, unless you didnt acclimate properly. Youll want to bring it up before you reintroduce the fish.
So. My question is, did you acclimate properly?
Also, whats your SpecGrav?

 

[azzala]

The PH is a little low. I normally keep it at 8.2. The gravity is .022. The fish were acclimated using the technique this sight recommends. All the fish had been in the tank for a month or more before the die off occurred.

 

[yvetterich]

did you recently switch foods? water changes? add anything to the tank you have not added before?

 

[azzala]

I have tried to think of anything out of the ordinary. I use RO water from a store in town, nothing new there. I feed brim shrimp and veggies all frozen and from the pet store. This last batch of shrimp is getting tossed out even thought when I asked the lfs about food being a problem they seem to think it was unlikely. They think a chemical from somewhere in the house made it into the tank. One guy at the store had the same thing happen to his tank but when I asked what to do about it he said he had sold his tank after that. That isn't the answer I was looking for