The label of the product has a guide "suggested feeding concentration ppm nitrogen"
and a column "periodic every 7 to 10 days"
You are mixing the 20%-750 ppm N and you say "plants are being fertilized every watering on a 4 day of 1 day on watering schedule." ( is that every 4 days ? )
"They are also being fed a slow release fert to supplement."
According to the Label, 750 ppm every 7 to 10 days is on the high end of recommendations, i.e. outdoor Garden Landscape. Thats for outdoor shrubs
If you are fertilising every 4 days, plus the slow release fert to supplement, you seem to be over the label rates
That would seem more than adequate, if not too much ?
The label says woody ornamentals 200 to 375 ppm or heavy feeders 350 to 400 ppm.
These label recommendations might be conservative, to prevent burning at high EC.
Also says mix in warm water to completely dissolve all ingredients.
You say, The plants are flushing new growth as well as flowering but I can’t keep them fed properly.
Can you explain this more ?? What symptoms do you see ??
Also how big are the plants and containers, and what type of mix are they in ??
How much slow release fert is applied ??