Lethargy followed by death = starvation.
Outside of discrete cleanup efforts, Turbos are really too big to be supported by the algae load in 99% of home aquaria. You're talking about what happens after they finish the cleanup. To have more than one in a typical tank is sorta crazy (if you're thinking of the snails' long term) unless you wanna be feeding the snails like they were fish.
Except for the largest tanks I really recommend keeping your individual clean up crew members as small as possible. In all tanks I would keep the crew as few in number as possible as well.
Cerith and Nerite snails are my favorites. (And my hitch-hiker limpets.) Only get enough to control (not eliminate) your algae.
Not a fan of hermits so I usually have very few - 0-5 per 50 gallons. I like blue legs, but I've seen little long term difference in performance between the CUC hermits. (None do as good as snails.) For any of these, buy as small as possible.
Astrea and Trochus should be considered "large" snails for most tanks. Many tanks that have good, steady algae growth can support a small number of these. (Ditto for other snails of similar size.)
-Matt