38 gallon established tank, a cin clown, diamond goby, Pygmy angel, gbta, a cleaner shrimp, a few blue hermits and turbo snails, the fuge is a lil over 3 gallons with new crushed coral, some macro algea and a 15 watt 6500k cf on it
You obviously have the fuge plumbed into the main display right? If so, there really is no way 3G would make a 38G tank cycle. And you couldn't have a cycle in just the fuge.
You are just going through an algea bloom in the fuge, did you use new sand? Looks a bit like diatoms, should go away in a week or so. Have you tested parameters? That would tell you if you are cycling.
I added a DSB to my fuge/sump setup a few months ago, had the same issue from new sand. No biggie, just keep up with normal water changes and what not.