yes we want the numbers for the ppm like orange said. what is the ammonia, nitrite, nitrate, ph levels? sounds like to me you are not cycled but levels say good. reasons levels will say good is because you have no ammonia in there to convert to nitrite or nitrites to convert to nitrates. you need these to have a good balance in there. it creates a beneficial bacteria for the fish so they can live. if you havent added any pure ammonia or fish that cause a bioload then your tank is not cycled although your tank may read alright. do not add any puffers yet. also do know there are a lot of puffers that are brackish water fish. make sure you get a freshwater puffer if you are doing freshwater.
doing a fish in cycle is cruel if you dont know what you are doing because you will stress and kill a fish. its like throwing you on another planet that doesnt have or barely has enough properties/oxygen/gravity, the necessity things we need to breathe and live. we recommend you going on a search on here and search for cycling a tank and you should get a few threads how to do and how to do it safely. just because you used someones filter setup DOES NOT mean you have the beneficial bacteria that you need. that was for their setup not yours. also, and someone correct me if im wrong, but after the filter dries up a little bit you loose your beneficial bacteria.
the snails that you have, did they hitch hike in off the plants or did you buy them? if they hitch hiked you will want to cycle your tank correctly and start doing it right away because you will soon be VERY overpopulated with those snails and you will want a good running tank and get those puffers in there so they eat the snails. they do not need to mate and will lay egg pouches everywhere with like 5-10 eggs in each pouch and you will start to see 100's of pouches then hundreds of snails. trust me ive been dealing with it for a year and a half now