toxic to snails?

[markfmvl]

I had my 90 gal. tank crash in July. A large engineer blenny died under the rock work, It went un noticed until other fish started disappearing. It had been a particularly busy week. We ended up loosing some chromis, a pair of clowns, tried to move my sailfin tang to another tank but the stress was to great and he didn't make it. we moved 1 chromis and a yellow tail damsel to another tank. We did a 20 gallon water change and cleaned up the tank and removed the dead fish that the ammonia spike killed. We didn't try to catch the neon dottyback and left the urchin and hermit crabs.
Well, despite the cleaning the algae took over big time. So the ammonia went to zero as also the no3. I wanted to get the tank back to normal, and as the spike took out all my snails. I tried adding a mex turbo from another tank. I was dead the next morning. Then when the urchin died we did another cleaning and water change (20 gal). I also removed a DIY sock holder that had some screws and a few aluminum rivets in it, cleaned a rock from the fuge that had a crab apple sized dead sponge on it. I also put some activated carbon in the sump. After a few days I tried a new snail, this time a margarita, but it passed out in about 15-20 min. I put it back in the tank it came from and got it revived. In the recent test, NO3 still zero as well as PO4. Dotty back ok as well as hermits. There are still nutrients circulating in the tank because the scrubbed rocks are starting to grow algae again. I thought of the possibility of some toxin being given off by dying sponge, or something in the pop rivets. The screws had some rust coming off them But the rivets seemed ok for the most part. Shouldn't the activated charcoal absorb any toxin from sponge? How long should it take? Any ideas?

 

[Randy Holmes-Farley Verified Community Expert]

Not all organics are bound by GAC.

Metals (e.g., copper) might also be an issue.

I'd also get a confirmation on the ammonia from a different kit.

Big water changes and a metal binder such as metasorb, cuprisorb or polyfilter would be a good choice.

Change the GAC. It can get used up quickly in an emergency situation with lots of organics in the water.

 

[markfmvl]

Thanks Randy. Good advice, I had not thought about things such as polyfilter. I still have pods in the tank so it seems to be mainly affecting snails at this point. The cheato is not growing much or struggling. so I think the nutrients are still low at this point 2 months after the crash. So at this point I am leaning towards a possible metal contamination from some rusty screws from a DIY sock holder that I removed before the last water change. Maybe they were zinc plated or something. Zn and Cu were listed as toxic, among other heavy metals in an article I found on heavy metal toxicity to snails... thanks again.