If so, they tend to feed on decaying matter. I've dipped some lps/sps corals that weren't looking good at all and tend to see them covered in amphipods. They're not eating the corals causing that damage, they're just feeding on the dead stuff
Depends on the type of pod. Copepods/tigger pods are very small and usually just appear as specks on the glass. Amphipods are much larger, 1/8" seems reasonable, pretty sure they can get larger than that