I've ostracods in my tanks, small ones of the "mostly harmless" sort. If you want to culture them thin slices of cucumber, red pepper or any dying leaf feeds them. They clear up the yellowing watercress leaves in my tank and develop quite intense yellowish pigmentation.
Despite their small size they are no good as first food for larvae. I think they shut their shells tight and pass through undigested and they cluster on dead and possibly living larvae. ( I tried this when my daphnia colony crashed as the axolotl eggs hatched-brine shrimp were needed). I did have one larger leucistic larva which ate them, grew well and went quite yellow, the colour fading when I supplemented with earthworms. If you want to try getting colour into an ostracod eating larva try floating some red pepper in the tank! You may be rewarded with intense pigmentation.
I think guppies clear them down to very low levels quite fast, there are very few in my one week post stocking guppy tank which was thick with them before I put the fish in. In general if there is no decaying vegetation they are thin on the ground.
Don't get too paranoid about ostracods, but be careful and have alternative foods handy if dealing with very small larvae.
