A clownfish is very very messy eater so the bioload makes it to much for a small tank.
I understock my tanks because of less chance of stress. Some fish just don't get along I have a lawn mower blenny that loves to pick on clown. He will pop out of no where and scare the clown they are in a 55 gallon with a royal gamma and a wrasse.
Five turbo snails are a lot for a 20 gallon besides that they like know knock stuff over and need lots of algae. I have 3 that I move around in 2 different tanks so they don't starve to death. You might like a couple of these instead Saltwater Invertebrates for Marine Aquariums: Banded Trochus Snail You don't have to worry so much of them not being able to upright themselves like the turban snail.
I understock my tanks because of less chance of stress. Some fish just don't get along I have a lawn mower blenny that loves to pick on clown. He will pop out of no where and scare the clown they are in a 55 gallon with a royal gamma and a wrasse.
Five turbo snails are a lot for a 20 gallon besides that they like know knock stuff over and need lots of algae. I have 3 that I move around in 2 different tanks so they don't starve to death. You might like a couple of these instead Saltwater Invertebrates for Marine Aquariums: Banded Trochus Snail You don't have to worry so much of them not being able to upright themselves like the turban snail.