Im brand new to growing hydro... so please don't take what I say into *complete* consideration... but I believe since the ppm should be around 400 or so for seedling lets say... then it would be MOST ideal for it to always be 400.. so if you could create a computer program or something to maintain 400 all the time.. it would be best.

I'm really interested in finding out the answer to this question too... :P
Illusion Reviewed by Illusion on . PPM Question So I just got a TDS meter on Friday and I have a question, but here is my info first: My tap water is around 300 ppm. I changed my res for the first time on 9/28 and added 55 ml of nutes. On Friday (10/5), my ppm was around 500 or so, so I added 30 ml more which brought it up to around 700 ppm. Yesterday (Sunday) it was down to a little under 500 ppm, so I added around 50 ml more nutes which brought the PPM to around 875. My reading tells me that 1000 PPM is about average, and 1500 and Rating: 5