do you know what species of copeods you're culturing?
i'm assuming they're harpacticoids..mandarins hunt harps. you can culture them without phyto. although having phyto in your cultures is definitely a bonus. you're gonna need to give the culture a few whiles, like a coupla months to get it up to a harvestable population. if you're seeding your culture from the live rock, remove it after you see at least two pods. there will be hydroids on it and they will eat your pods, killing your culture. also, don't use the same water that the rock was in unless you filter it. you'd be surprised what's swimming in there that you don't see until it's too late.
using a bacteria food base i find is far more productive than phyto. phyto seems to regulate the water chemistry more so than being a food source for harps. i discovered this leaving bs cyst husks in my bs cultures. the harps feed on the bacters and bloom... give it a try... set up a bottle of sw, add bs cysts and a few drops of phyto. introduce some harps. you'll be harvesting the bbs first, then let the bottle go until you get a decent population of copepods. you'll need a few bubbles a second to roll it over but not too bubbly.
ammonia wlll encourage a phyto bloom. ammonia is a phyto food. it is nitrogen.
another food source is bakers/brewers yeast. but yeast is easy to overfeed and kill your culture. make a 1 ounce solution sw and a few grains of bakers yeast out of the packet. the sw will kill the yeast, yet preserve the cells for you pods to eat. use a few drops to lightly cloud your culture water. easy to over feed this stuff unless you're polycuturing brine shrimp with the pods.
this is where the phyto comes in handy. it feeds on waste and will provide a veggie food for your pods at the same time. green water is good. not dark green. dark green means you've got too much waste, although i've never really let my cultures go too dark.
you're gonna need a rack of these cultures to sustain one mandarin that is not trained to take other foods.
this might discourage you. it discourages a lot of folk.
harvest is easy... but a pita.... use a syringe with rigid air line attached. you'll have to suck up a few hundred a day to keep your mandy fed.
if this is discouraging, i suggest obtaining a mandarin that feeds on frozen foods, or live baby brine shrimp. if this seems too much, perhaps trying another fish.
but i do suggest culturing pods and other planktons for your reef.
hope this helps you and others interested in culturing copepods.
