My 55 gallon res doesn't seem right but I may be wrong. I am coming to 41 days flower and my res is kind of high at 1500 ppm. My plants all seem very happy and healthy, but my ppm rises slightly and doesnt lower it even stays the same for little periods. So only a lil fluctuation but its always up. My ph is set to 5.8 and I let it drift to 6.2 which does so pretty slow. So ph fluctuation is cool but why does my PPM not go down ?
As the plants drink more water than they use nutes the PPM will rise because the nute to water ratio has shifted. Mine does the same thing and when it gets too high I dilute the res with plain or pH'd water depending what my pH is. My guess is this is normal.