As stated above, Nori or a product such as Seaweed Select for which it can graze on 24/7. Also Z. flavescens are little pigs as they'll eat just about anything. Try feeding shreds of meaty foods such as shrimp, squid, mussels, etc. a couple of times a day.
Also, you might try live brine if you can get it, or raise it. Use that to get the fish to feed and put in the frozen food at the same time. Sometimes the fish doesn't realize that cube shaped glob is food and needs a little help.
