Losing battle with aptasia

[Beverly]

My BB 37g monti cap tank has 175w MH, ~20 lbs lr, 4-5 snails, some non-invasive macroalgae, at least one small hitchhiker crab, and no fish. This tank never gets fed, but does get kalk dripped nightly and Mg added when necessary.

So now I'm finding aptasia growing in a few places that are hard to get to How can this stuff grow with no food?? Are they simply photosynthetic, or can they survive on detritus?

Think I'm going to get a peppermint shrimp or two to solve the problem, but am still stumped as to why they are there in the absence of real food

Can anybody shed some light on the lives of aptasia?