A sea hare take the algae down to the roots and will even pull most of them out as it eats they are very good at what they do but this is also why they will starve. snails eat what is on top and if it is to long they will leave it be unlike a sea hare. and 6 turbo snails in a 90g will not be enough in my opinion I had 6 in a 55g and had to add more snails. I didn't add any to my tank when I up graded because there is a hundred or so steminila snails on the rocks that has lessened Carpet Nem ate them quite often. If you get a sea hare let it do its thing for a week or so and pass it on or return to the store. do not keep it to long it will starve and die then it will nuke your tank.

Bill