You don’t need a flushing product just use tap water.
Put your plant in the sik or tub and run water out of it until the ppm is like 300 or 400 coming out the bottom.
Your using fox farms so the first thing is to find out if your ppm meter a 500 or 700 scale, probably a 500.
So then you look at the feed chart, look at what week of life your plants in and that’s what ppm you should feed. The chart should show you what ratios to roughly get there but check with your ppm meter to make sure, then PH then feed and when you feed that 5 gallon bucket you mixed ip of nutrient water make sure your plant gets 20% run off or salts will build up in the root zone, your PH will slowly go out of wack and your plant will end up in nutrient lockout.
Sounds like you need a flush and a fresh feed right after.
Here is the 500 scale modified feed chart because fox farms shows theirs in the 700 so very confusing.
Hope this helps.
Thanks for the tag @Budz it’s good to know when someone more sober shiuld be driving the mongoos down the road lol