Using all FF nutes on their feeding chart except wholly mackerel and kel p me kelp you. Does the EC/PPM at the top correlate or are they used individually? In other words should I use EC if checking with a TDS or PPM? If I add nutes to get to say, 1.8-2.1, should my PPM be at 1260-1470 or are they not calibrated together? If I adjust to the recommended EC, my PPM is quite a bit different.
Many thanks!
They should be the same. But I think FF uses the 700 scale for ppm and I bet your tds meter is a 500 scale. So that would make a difference. I would use EC if your pen does both. There use to be a conversion chart someone made to show ppm on the 500 scale for FF nutes. I dont have it anymore.
EC directly relates to ppm. As axeman stated there are different scales. This is a chart I converted to 500 scale from the 700 scale fox farms uses
This chart shows the relation of ppm to ec on 3 different scales.
500 scale means 500 ppm = 1ec
700 scale means 700 ppm = 1ec
My pen does both and there is a conversion chart on the back of the FF pamphlet. It has two tables - Hanna ppm 500 and Truncheon ppm 700. I appreciate the education. Probably explains why I’m seeing some yellowing and curling on my leaves. I’m at the end of week 5 of the bloom stage and have some really nice fat buds. Don’t want to lose them now! My runoff PH got quite low, around 5.2-5.6. I did a flush with 7.5 PH water (about 3 gals) then gave them a shot of cal/mag with some boomerang and bembe. They look a bit better and my runoff PH is about 6.6 now.
I appreciate the quick reply!
Have a great week!
Many thanks. I know I should not have smoked as much and paid more attention in science /chemistry class. 
Love the forums and I appreciate you guys (and gals) immensely!
Have a great week ahead!
About time they started doing that
