Just a couple of observations...

Likely time to transplant. When you do, keep soil level to within about 3/4" - 1" from top of pot. The surface roots need the fresh air circulated across the surface. A lower soil level prevents air circulation.

MG Africal Violet soil mix has a initial nute content of 5-5-5. It says after 30 days, to suppliment the nutes. Would do so right after transplant. (asap)

Would lose the African Violet nutes for acid-loving plants. The peat in the soil will keep the ph down already...using this stuff might just be causing nute lock-out, likely causing that yellowing you tried to correct with the magnesium sulphate. (epsom salts)

You will want a fert in the 6-4-4 or 12-8-8 range, or so, for vegetative growth. You might want to look into aquiring some micronutes, also.

The Schults Phosphorous...is that the 10-52-10 stuff? If so...that's a really strong bloom fert. Would begin use at a lesser dilution rate, once you switch to 12/12, and get used to the product's effects on the ladies. Using a bloom fert in the 2-4-6 or 4-8-12 range is easier to work with.

Knowing your run-off ph would be a big help in keeping your ladies happy. :jointsmile:

HTH...Rusty