depends on what system you use

i use autopots for my hydro system, but they work with organics too

autopots eliminate ph/ec maintenence, and even the need to res change at all! they use no electricity at all, and can completely automate your grow for weeks at a time if you so desired... do a google on them or the smartvalve mk2

they aren't the perfect or greatest system in the world, but they do a damn good job and for pennies compared with the alternative to fully automating your grow... all i ever do is refill my res a couple times every grow when it starts to run low

i wouldn't grow again without them, i use them for all my plants, mj and otherwise