Hey there! I wouldn't use that water just in case. Also, I wouldn't ph the water untill feeding, as it can fluctuate over time. Also not a good idea to premix nutes. Nutrients will also change your ph, so it's a good idea to wait some time untill after your nutes are added to ph your water. I fill my buckets a day or two before feed and let them sit, as they release chlorine. As far as I know, there's no need to add anything to them untill feeding time. Happy growing!