I find it hard to believe your mandarin is plucking cyclopeeze out of the water column, so if it's getting any, it will be what it finds on the substrate/live rock.
I find it hard to believe you'll have enough space in your tank to keep enough live rock to keep your manadarin going. The volume of refugium required to keep enough pods going to feed the guy will likely take up most, if not all of the tank. You have 3 options
1.Buy pods, or attach a large enough refugium, which is likely a 10 gallon.
2. Return fish to larger tank (either yours or elsewhere)
3. Starve it to death, which is what you're doing now.
There is a guy in the book Ultimate Marine Aquria who has 3 or 4 similar dragonettes in a 40 gallon, however if you look at his setup, it is a dream for them, with a LOT of live rock ,and a gallon refugium I tihnk, and even then he doesn't recommend it.