still very slow

My fry from June/July don't seem to be growing as fast as I'd like

I think I'm doing it right, they have at least 3 small feeds a day, I'm doing water changes daily if I can, sometimes every other day, but the rubbish gets hovered up if not. They're now spread out over 4 tanks, I have to say slightly more crowded that ideal, but I'm doing my best. They have micro worms for the smallest ones (they all had brineshrimp to start) with flake foods, the bigger ones get flake foods or granules and some frozen cubes a couple of times a week.

The biggest have bodies about 10p size, but some are stuck at peas!! They are blues, and they do have a pearlscale parent, as yet I don't know if the other parent is carrying the ps gene, so I'm hoping these are factors to their slow growth rather than me??

I've seen a recipe for beefheart mix do you think this will help or am I asking for disaster if I try something like that?? Is there a super growth food I can try or am I just being impatient??

Blues are slower growing than many varieties......
Pearlscales are slower growing than many varieties......
Blues Pearlscales are even slower growing
and for really slow growth you could add blushing (paraiba) or double zebra into the mix.
10p size sounds quite respectable for 3-4 month old blue pearlscales. Giving them more space would help, as does segregating the different sizes, but ultimately some of the smallest probably won't grow, or if they do, will turn out to be poor quality & or deformed.

So if your space is limited, the question is, "Are you prepared to continue limiting the growth of your best fish by devoting space to your worst?"