Frog, I thought you knew this little factoid already and maybe you do but for those that are we or whatever, here is how you determine EXACTLY how much nutrients are being given to your plant and how you should be mixing in your nutrients. I'm not going to go into the why you should cause I just got out of a really hot bath and I want to conserve strength so I can rub one out before I take the kids to the movies.
Fill your Rez at LEAST 3/4 full before adding anything!
Add your Macro nutes and let mix around (u DO have a pump running 24:7 in your Rez right...)
Add micro and anything else you think is goIng to fix the fact that you really don't know what the fuck your doing
Top off with tap to the desired level
Mark THAT WATER HEIGht with marker
Let mix for 20. CALIBRATE your ph pen, test ph.
Add your up or down..that has been DILUTED at least 10:1 from the bottle strength. If you see a little cloud form when you pour your shit in there it's waaaay to strong. Don't do it.
Let mix and test again. Yadah yadah.
Ok let's say your ppm is 1030 and your ph is 5.6 ( like mine was 4 days ago)
You come back the next day, the water is lower and now the ppm is 1080 and ph 5.8. Still ok to me.
Next day, even less water gone, ppm at 1150 ph 5.9.. Ok, now it's time to take a break from watching German fisting porn and give your plants some love.
Add clean tap only to the fill line you marked. NOW test the PPM. Wow it's 960. Now you know that your plants absorbed 120 ppm of nutes in 4 days. 960 is pretty close to the original 1030 so I'll probably leave it for another day.
Now I'll come back the next day, there is like 10 gallons of solution gone so to get me back up to the original 1030 or close, I'll mix like 5 gallons of fresh nutes in the exact proportions I did originally and add it in the Rez. Test the ppm, if it's higher than you want but not by much your golden because youll top off again with tap to the fill mark.
The main point is this folks: the only ppm comparisons should be done when the rez is at the same height! Plants transpire water and leave the minerals, its normal for ppm to climb because of this.
In veg I'm pretty lazy and I use root excelerator which is expensive so I do this for several weeks without changing the Rez. In flower, I maybe go two weeks tops. Because I'm such a fuckin dope Mack daddy I typically top of with fresh water everyday because I plumbed my grow set up so my filtered water comes out to a hose bib about a foot from my reservoirs. I fill test and RECORD ppm daily simply because I don't have to lift anything and risk injuring my jerk off hand. This allows me to track exactly how much nutrients are being absorbed every day.
Make sure you change your flowering Rez every week or at MAX. Every two weeks. You can never know WHICH mutes are being absorbed and if you keep adding back nutrients, the PROPORTIONS between the minerals can get fucked up am lead to lock out problems. This is why I hardly ever just add macro or just micro to my Rez. I always add balanced nutes.
Make sense? Anyone that learned anything now owes me rep cause my wife is calling for me now and I never had time to "spend a little time with myself" cause I was typing in my I phone