Snail population dying

[Method]

My population of MTS seems to have mostly died off. As in I see empty shells but very few active adults. I still periodically see babies. I have an Amazon tank with pH 6.8 and kH 3 degrees. I have a healthy group of ghost shrimp, and a population of pond snails (I wish they had died off instead of the MTS).

My main suspect is too little available calcium for their shell deposition. Has anyone ever tried putting marble chips in either the tank or the filter?

Other potential problems:

About two months ago I dosed erythromycin to get rid of BGA (worked like a charm). Even if this was a problem for the snails at the time, I don't think it is now. I've done quite a few water changes and have kept clean Purigen in my filter since then.

At one time my rather large piece of driftwood was held down with a brick and copper wire. I don't think the copper should be any more of a problem now than the erythromycin, for the same reasons.

I only feed my fish once a day or once every two days. Still, I have a hard time believing that mature MTS could starve.

It is possible that I have anaerobic substrate. 1" of MTS, capped with 1.5" of river sand. When I poke the sub I see bubbles, but they have no odor. All of my fauna, except for the MTS, are fine. I've never lost a fish in this tank (about 6 months).

Any suggestions?

[diwu13]

Why do you suspect calcium deficiency? Do you see holes in the shells of the pond snails or in the empty MTS shells?

I believe copper would oxidize in a fish tank, could be wrong though. I know the only "safe" metals would be zinc and stainless steel.

Also, you use MTS to aerate the substrate. They'll dig as far as there is oxygen content in the sand.

[Method]

I suspected calcium deficiency solely on the basis of the 'slightly' acidic pH and the low kH. I do dose trace, but I figure the plants get most/all of it.

I figured that Purigen (and carbon to clear the erythromycin) would have absorbed any copper.

[diwu13]

If you don't see holes in the shells of the other snails it's probably not calcium deficiency.

If the copper does leech something poisonous in your tank I don't think purigen/carbon will absorb it fast enough. But it's probably not that either or else your fish and pond snails would also die .

No idea what's wrong really :\.

[DesmondTheMoonBear]

Are you sure you didn't just have old adults die off?

[Method]

So I originally got ~40 snails from Petsmart and put them in my quarantine tank. I waited a month, then took about 20 and put them in my display tank. Granted, the ones I transferred may have been biased by age (easier to see and catch large ones). Still, I'd expect to see many more adults in my display tank than I currently do (maybe 3).

It also seems that the dead ones are in more age classes than just adults.

The thing that really gets me is that I still have a healthy population of pond snails and *some* MTS. Maybe I AM underfeeding...

[wetworks]

Get a polyfilter, put it into your canister or HOB. If you have anything toxic in your tank, the polyfilter should be able to pull it out quickly. Plus, when you take out the polyfilter it will turn color to tell you what was in your water. If there is copper present the polyfilter will turn blue, for example.