What kind of light are you providing them?

The plants are large enough you should provide them with full strength solution. In fact, the diluted solution may be hindering their growth. I can't speak to tomatillos, but peppers seem to like a lower nitrogen to phosphorus ratio. Incorporating the maxibloom will probably help this.

You mentioned transplanting them into 6" pots. are they in soil or in a hydroponic system? I'm a little confused by what I read. However, those plants sound kind of small for that age.

I'm sure they're too small, but considering that I'm growing them in a closet on a limited budget, and for the first time, I'm pretty pleased with myself :)

I had some old aquarium lights hanging around, but they are short length T8's. The first set I used was two 36" 20W, then as they got bigger I used two 48"(?) ~ 30ish watts. I moved them up to a light that usually used for photography yesterday (6 50W CFLs, 300W total, used as a soft fill light). I should have a proper 600W MH by the end of the month though.

As for medium, they've been in a 50/50 perlite/coir mix since germination. Due to budget restraints, I'm using a simple feed-to-waste system, but I have a EC meter coming in so then I can move forward with constructing a basic flood drain system by next month.

What ratio should I use for the gro/bloom mix?