That same chemical is also used to clean pipes by killing invasive roots. I've heard of it being used to kill stumps, but wouldn't want to garden around there afterwards. ;)

For more on common chemicals easy to overdose in aquaria see:

http://members.optushome.com.au/chelmon/Chemicals.htm

There can be residuals in the gravel some time after it was administered and water changes begun again.

Chelated copper is supposed to be less toxic than copper sulfate, but also may remain in the tank longer. I asked the originator of this post if the product he was using was chelated, but he was more concerned about the indignity of having a log voted down, than answering the question.

If you use it, also be prepared to do a lot of water changes. Since it sounds like there is an annoying number of snails in your tank, that could be a fair bit of rotting meat which needs to be siphoned out.

Snails can be a terrific nuisance. Of course a bloom of snails is a far better way to learn that you are overfeeding your fish that to deal with a bacterial bloom or outbreak of a disease among your guppies.

It may be that you would rather leave a piece of over the hill lettuce in the tank. Rinse it and drop it in. After a few minutes pull it gently from the tank, along with the snails now on it. A couple times pulled and rinsed and it may help with the snail over population.

Especially if you feed live or frozen or freshly hatched brine shrimp, you want snails in there. Having some snails on clean up patrol may protect your fish from some disease, especially a bloom of velvet. I wouldn't have a fry tank without small pond snails. Snail poop is a lot less dangerous than decaying shrimp.

I may have made a mistake making a conciliatory gesture or two towards Urbanres. Already annoyed, he then seems to have resented that. That wasn't the plan. :(