Your right that some prey on small crustaceans and what not. Others feed on algea. Small fish like wrasse will feed on them.So I managed to find where someone posted a video of marine mites in the algae in their overflow. The fact that I know of two tanks now that have marine mites in the overflow makes me think these mites feed off of pods. The mites are at least 20x smaller than my isopods. They might predate on amphipods. I doubt they feed on copepods however since they’re quite a bit smaller than the mites. Mites only eat the fluids of their victims so I don’t think they’d bother with the small amounts of fluids they could get from pods smaller than they are. They’d have to work much harder catching smaller pods when one isopod would be much easier.
Last night I decided it was time to increase the flow from the return. I originally cut the PVC in the return pipe about 3/4 of an inch short. I left it that way because the return line had a leak in the silicon where the pipe goes into the DT. I fixed it using J.B. Waterweld. It’s reef safe and binds to both glass and PVC. It’s held up quite well. I cut a 3/4” piece of PVC and slipped it on. I’m definitely getting more flow now.