my local grocery sells 5 gal bottle for a few bucks,and the machine i fill um with right outside,1.75 for 5 gal,mix that with your tap water and things will turn around for you like dirt bag said,i had same problem but was outdoors doing same thing,with rise and fall,i was using tap water,when i finally figured it out that was what was spiking my mix,so went down and got 6/5 gal bottles of ro water filled the 33 gal can grow,ph and ppm was perfect,had 6.0 ph 850ppm after i added my cal nit,mag sul,feed,perfect,but 2 days later went to spiking on me again,so a friend here aqua man suggest,get some potassium bicarbonate,i did,but first off i had to rinse the roots real good and give the plant and 33 gal of water a shot of hydro guard,that straighten it right up,when it stablized i then used the bicarbonate to keep my ph were i wanted it and when ph is ideal at 6.0 i was then able to bump up my feed to 1000 and hold it there,every 2 days i had to top off the can ,but always with the same mix as the begging ,just had to do some math and break every thing down to a small scale and for 5 gal of feed each time,but never did i just add water and have any luck