Indoors I prefer coir (but am still aiming to give Pro-Mix and Sunshine #4 a try someday). And the reason why I don't [gauge media conditions] is because I tried to solve problems using that method and it just wasn't working. I also found myself chasing numbers when the plants appeared to be fine, and I've had
way too much experience in fishkeeping with how well chasing numbers can go--you've got to go
first by your own observations of the organism in question.
Now, with regard to your feeding regimen, it's been a
while since I've done synthetics, so I want to be sure everyone is clear on that. Thus, I have never used Jack's. But to me synthetics are the same in a few regards, so I think I may be able to help you here but if there's someone with direct experience who says otherwise, go with them, k?
What I would do in this scenario is
first make 100% sure that your meter is properly calibrated. I use the two-point calibration method for pH, and the appropriate solution for EC. I also don't use ppm or TDS, I go with EC. Mentally it's a big conversion, but if you keep switching (or simply keep your notations in both ppm and EC) then you'll get a feel for where you want things to be. Now that that's out of the way, I would drop the strength of the feed a lot more than where you're landing, I would go with around 250ppm @.5 conversion (that's what...? .2-.3EC?).
I would
also perform a few slurry tests, taking media samples from various depths of each pot, including upending some plants and getting some of that from the middle of the root zone, assuming you're able to do that--if in something like a
Smart Pot, then that would be a pain in the ass and traumatic for the plant, so I'd just dig down the side.
Slurry test is outlined in og dmc's thread
Botanicare COCO Bales by a
Botanicare rep (or something like that), and briefly:
Well mixed sample set from all pots to be tested in something like a cup, if possible get samples from top, middle and bottom (can be taken from the side of the pot).
Have about a pint to a quart of RO or distilled water handy, test the temp, pH and EC of that sample.
Note those parameters.
Add enough of that water to your media samples to create a very wet slurry, you should be able to see some water above the sample.
Let that sit for 7-10 minutes, then retest.
Now you're going to have a much better idea of what's actually happening in the root zone, not just what's being washed out.