Just for your bank of information guys I run an eighty gallon resi that has held solid for 2 full weeks now. When I do my full strength add backs I add the water first and then add in the required nutes. I am not trying to be exact on my ppms. I try to get within 100 ppm of my target range at finish.
I then check my ph and it has been right where it needs to be every time.(5.8-6.2) I have been really pleased with how it is reacting. I am figuring it is due to having such a large resi.

Thanks again Bear

Good luck to you hound -Jay