Not sure how you normally do your water changes. Once you have done what you’re doing, I would leave it about a gal short so you can mix your nutes with a separate gal of water and then add that.
What EC/tds, Ph, Temp?
What wattage lights are those?
How offten do you water?
Ppm700 ph6.1 now 600W x 4 light
I only flood once a day.but It may change according to the situation.