If they are indeed trumpet snails, don't worry about them. Let them run their course naturally, they are actually good biological filtration helpers. They feed on detritus in the gravel bed and on top, they won't harm your plants. I wouldn't commit to a clown loach unless you want a big fish eventually (they grow pretty large). I had a huge wave of them once and then over the course of a month they leveled off naturally. The zucchini trick is a good way to keep them in check.

Say no to chemical treatments or killers. And bleaching is pretty bad since its basically like starting your bacteria culture over again.

i dont know if anyones mentioned this but putting in a copper addative helps kill invertebrates in any tank. you can find safe copper addatives at a local aquarium that are safe for your fish and wont harm them or change any alkalinity or any thing else in your tank. hope that helps

There's already so many useful comments on this post that I don't have much to add except that I like snails; certian kinds. I like the little cone snails that hide (for the most part) during the day in the gravel and come out at night in mass to clean the glass and plants. These are not destructive to the plants as some kinds are. I also like the ramhorn snails which also clean the plants though sometimes too well. Tender plants can develope holes with these, but they didn't do enough damage to worry about for me. I bought three clown loaches anyway and they did a great job getting rid of my snails, so great that I had to put them in another tank so I could get the snail population going again to try to deal with an algae I have a problem with. Clown loaches can grow very large but for some reason my three have stayed < 3 inches for the last 2 years, and they've been housed in my 100 gallon tank??? They're healthy, active, and eat when I feed my fish, so who knows.