Applesnails!!
Bridgesi (or just "brigs") in particular. They're sold in 90% of pet stores as "mystery snail" and come in gold and black commonly, plus some other fantastic colors including purple, pink, blue, etc

Size: roughly golf ball.
In my experience, they don't eat healthy plants, and will eat soft algae from the glass. Naturally, if you feed them too well they won't eat any algae, but you should feed them some sinking food or they will probably starve.
Best part is they require a male and female to reproduce, so you won't have to worry about them filling your tank with snails unless you keep more than one per tank. (I only have two and they just happened to be male and female so they mate like crazy).
I love these critters, so I don't keep them as clean up. You can find tons of info on them at applesnail.net to decide if they're what you're looking for.
I think they are ok at that temp, but check if you decide you're interested.