Sorry it took so long to get back so I hope your situation has improved. However, Pyramid snails don't rely 100% on clams and snails as a food source so even if you left your tank fallow there's till going to be something for them to feed on.
Someone help, I’m new to the hobby on my second tank 135g. Running sump system with refugium, UV light/ protein skimmer/ calcium reactor/ and gfo reactor. Recently purchased 2 clams and this one appears to have a whole in to I can see inside. Someone help me figure out what’s going on.