Can I put a small rock from outside into tank?

You can move a snail, but I don't see why you would want to in your case. It will either find the algae you put in on its own, or find other algae to eat.

 

I think almost every response here holds merit. If it fizzes don't use it. If it fizzes, use it. I wouldn't worry about feeding a snail. If it looks like it has rust or metal on it, don't use it. Why not use a mag float.

Every answer makes sense. If it fizzes, it's breaking down. Some will do this with sand to test if it's calcium based or not. If the sand deteriorates to nothing, that's a good sign. If it's a rock, though, maybe not so much. Rocks of the igneous and sedimentary variety can be made up of different layers of different materials. What if the rock was sitting in a copper mine millions of years ago? The outside may be harmless, but the inside might not be. Bad news.

I wouldn't worry about feeding a snail. Come to think of it, neither would I. I've never heard of one dying of starvation, although I suppose it's possible.

If it looks like it has rust or metal on it, don't use. That's good advice.

Using a mag float, now that's darn good too! Why pay for a veggie clip or weight it down with a rock? The rock would hide some of the food anyways, which would mean it would break down into ammonia eventually if not removed.

Wow! Talk about asking a question and getting some great responses!

 

Heh, man I put him on there hours and ago and he is just pigging out! If he WAS starving, he isn't anymore rofl. I think he fell asleep eating.