the recommended amount is a whole 2.3mg pill for that size tank. I used that amount and wasn't happy so i used 1.5-2 -> 2.3mg pills and it seemed to do the trick a bit better.
i have a 40g too.
defiantly do atleast 3 doses. i did 3 and noticed a few (3-4) left after my last dose so i dosed a 4th and havnt seen them since.
i warmed the water that had the interceptor in it (to help it dissolve more) and blasted them with a turkey baster. i did a water change on the first and last dose and ran carbon 12 hours after i dosed each time.
good luck, it seems scary but the only thing you need to worry about is crabs, shrimp, pods, etc. when i doses the sps almost opened up more and after everything was done they looked so much better.