your LFS should carry vitamin C to dose with in liquid form... when you spot feed you take a cup and some frozen cubes of misis or brine shrimp put the cubes in the cup then fill the cup up like 1/2 way with water out of your tank, let the cubes melt, use a turkey baster to suck some of the water/food up, then stick the baster in the tank and squirt it on your zoos, i ususally turn my flow off during this part and for about 20 min after.