I'm not sure there is much of a problem here as they look pretty good, but since you say that they're not bulking up the way you'd like, I suggest you consider the problem to be your soil. Doesn't MG soil have a lot of fertlizer to it compare to others? And if so, the extra feeding isn't necessary. So... I'm guess that what's going on here is that they appear to be finishing to early because of high phosphorus content of the soil. Maybe flush with a good deal of water, then let the soil dry out and see how they respond. Maybe the red hairs will stop and bulking up will take place. Happy Frog soil next time, or something similar. As Weez mentioned, maybe some more light like a sodium would help.