Quote Originally Posted by zero0ne
so the real benefit of having a PPM is knowing when to add more water to what you already have, and also being able to easily figure out how much more you need to add to keep your nut ratio at whatever % you want it at...

makes sense now.
remember the plant will use the nutrients it requires and leave what it dosent. You can only top up for so long before you will be left with too much of one thing and not enough of another, it can also lead to nutrient lock out if you get a build up of one and build up of toxic salts (faqs). I change once a week'ish. I top up once with full strength then once with 1/2 then just plain water, once ive put in the same volume as the res holds i change. Ive read various methods though..this works for me. but you need to do a full change atleast every 2 weeks..when i left for 2 weeks (topping with 1/2 strength) the plants didnt look so good!. Im new to dwc though.