What he said... believe it. When I read your OP, I said, here comes disaster. One month is a young tank regardless of what source of bacteria you start with, it has not cycled. It is in a very vulnerable stage where one addition or undetected death can be the tipping point. I'd reduce the bioload immediately and take it much more slowly. I wouldn't wait until a fish starts looking bad or you detect "signs". In fact, if someone asked me to keep sick fish in my tank, I'd say, not a chance. Not that I'm not a nice guy but it's just too much risk to my investment.
Second, those brittle starts are valuable assets to your tank. They will search for and eat detritus. Let them be... PS. A harlequin is not a good choice for such a young tank (and IMO many other tanks); the fact being that they are messy eaters and require "large" starfish to thrive. Just don't go there please. For future reference, my Hoven's wrasse loves those little brittle stars, now if I can get him to eat those pesky Asterina.
Good luck. Only bad things happen fast in this hobby.