Here is my standard spiel on peppermints, so my apologies if you have heard it... First, where you get them from matters... direct from the Flordia Keys for L. Wurdmundi are the best... the others are suspect... so if you get them from a wholesaler or store that might have gotten them from Texas, Miami or Tampa, then they might not be as good. They also will tend to eat the ones in hiding first since they hate to really come out... once all of the easy ones are gone, they will usually tackle the ones that you can see and hate. They will not tackle big ones, so kalk those... I have never seen this, but heard that they can be eaten by larger aips. Usually when I get a stable group of peppermints, I will nuke all of the ones that I can see with kalk and then they seem to clean up the rest. Then I have a good 3ish years until they all die of old age and then the aips start to grow in numbers and I have to order a new set of them and start all over again.
I would caution anybody never to get rid of a fish or peppermints that actually do eat aips... they always come back once you get rid of the consumers since they can hide out like cockroaches.