Might need to refresh the page. There is a picture that I added after the initial post
Hard to tell from pic, but possibly gammarid amphipod. Give that a quick look on google and compare images there to what you are seeing.
Are they beneficial or harmful?
They make tasty snacks for fish, eat micro algae and detritus. They can annoy zoas if they get over populated, but I have never seen then damage any. Just walk on them and annoy them. Their population is usually regulated by food supply and predation.
I definitely think they're gammarid amphipods, I have two clowns, 2 dot blenny, and a mandarin dragonet, but he's pretty small. I have a 20g long so I don't think I'll be adding any more fish. I also have a few snails and an arrow crab. Do you think any of these will eat them?
Clowns may from time to time, and same for the blenny. They are too big for most mandarins. They eat smaller pods like copepods. In addition, unless you have a captive bred mandarin, a 20 long is not much of a breeding ground for smaller copepods. With that said, you may need to supplement the tank with copepods for the mandarin. They are eating machines and can decimate a pod population very quickly.
Yeah, I dose the tank with pods and put phyto in daily to feed them :) I did my research before getting the fish and it was the last fish I added, so whatever pods were in there from the liverock/overtime I've been adding to them
