Contrary to what a retailer might tell you I dont belive there is a 'magic amount' of snails and hermits.
Some places might suggest 1 snails per gal
and 1 hermit per 2 gal
. Another place might say 1 snail per 2 gal
and 1 hermit per gal
I have maybe 10 snails max in my 20 at this point and run my algae magnet over the glass maybe once or twice a week. The 80 has a whopping 2 snails and I run the algae magnet over it every few days aswell.
The more "inbalance" your tank is the less you have to rely on algae removing critters.
starfish and snails serve different purposes.