If you don't have a EC of TDS meter you should top off the rez with PH adjusted, distilled or RO water with nutes pre mixed (1/2 strength), most of the loss of water is from evaporation. The evaporation leaves the nutes in the rez and this means higher PPM, and can burn the plants. I find that if you change the rez every week, you don't really need to worry too much about this, maybe make a habit of adding 1 gallon of distilled or RO water with nutes pre mixed (1/2 strength) halfway through the week. For example: I change the nutes on sundays, and on wednesdays I add 1 gallon with nutes 1/2 strength nutes to each 6 galolon rez, and I have no problems with my PPM levels. I start the week at ~475 PPM and by the end of the week I have ~300 PPM. I use DWC style hydro.

You should post some pics for us to see.


L0rdsOth