Thank you for the reply. I've read over your articles/posts a number of times when I found this forum. Before that I was going strictly by the cocoforcannabis.com guide, which seems to correlate well. Until I got to flower, I had no issues with feeding and EC, and things went spectacularly well. See
https://www.thcfarmer.com/threads/explosive-growth-in-coco-coir.136487/
Before veg, I was seeing runoff EC lower that input, sometimes more than 400 points. I guess things were really sucking in the nutrients. Possibly michorrizae as well as coco sucking up cal/mag? Anyway, watered 4x daily and all was well.
Then flowering - a couple of things changed then. I dropped lights from 18/6 to 12/12, and I changed to flowering nutes (using GH, started with
Foxfarm), and I started adding some H2O2 to the mix. Suddenly my runoff EC was higher than input, as much as 400 points. About this time I also added a 6-inch input duct fan running 24x7. Lots of air volume dumping in next to the Airpots keeping that area between 72 and 75F all day. I'm sure it's increased evaporation near the pots some.
I added a 5th then 6th, then 7th feeding. I started dropping input EC. I increased the amount per watering. In four #5 (3.5g) Airpots, I was getting 5-6 gallons of runoff each day, which seems like it must have been 7 g/day input based on how fast the reservoir had to be refilled. Even then my EC was higher! I ended up doing ecen more of a flush by simply running 7 gallons (all I had in the reservoir at the time) of water through my 4 plants until I ran it out. Then refilled with EC down 300 points. Finally ended up with runoff EC about 1000 with input EC about 1000. I've not figured out exactly why my EC kept rising, but I did find some anomalies.
For one, I'm not measuring correctly. I wait until the pots drain and the sump system spits out the runoff into a bucket. I measure the bucket, which has averaged the pots with each other and some of the previous runoff. But at least I get an ongoing average.
Second, I don't know what input I have. I didn't measure my halo drip system until late in the game, and I can't pull them out now (for measurements) because the trunks are too big. I pulled one briefly early in the grow and estimated something based on that. But now I just look at how often I fill the (30 gallon) reservoir. I'm putting in 5-7 gallons per day, and I'm getting at least 3 gallons of runoff. Usually EC is about 150-200 points higher than input now.
Third, what seems a huge issue that I've recently discovered. As the water level lowers in my reservoir, the amount of water coming out of the halos changes drastically. Possibly decreases by 2/3rds.
Fourth, after time I wasn't getting the same amount of input or runoff from each pot. Tweaked valves there, rubbed halo drip holes. (One reason for adding H2O2 was to control algae and possibly help clear halo drip holes.)
I seem to have found a happy medium with input around 1000 EC with 7x daily feedings, adding some extra watering here and there manually when the reservoir is low. Now I'm settling in with output EC around 1200 or less.