I change every 7-10 days. Thats whats weird is that as the the plants take up the nutes my ppm should go down but instead its rising. I am thinking since water is being consumed through the plants and also through evapration that the nutients per water ratio is whats changing the ppm to rise. Meaning I am thinking the nute ratio to the water would be higher for the amount of water thats in the res. I bet if I just poored a gallon of Ph'd water with no nutes into the res my ppm would lower. You smell what im steppin in?

Peace