D3V'-- OK, lots to deal with here,...
--- firstly,
soils have been very iffy these days, with many bags showing badly acidic pH, ..talkin' low 5's here!
... some still get OK bags, but it's a craps shoot frankly,.. I've had many peep's here with troubles with pH issues stemming from the lousy quality control they show anymore! The only decently accurate way to test soil pH
in-pot (run-off method is bollocks in general) is to use a soil pH probe; Accurate 8 makes a good one for the money,...
--- water! ...for certain chemistry related reasons, using a pH meter on RO/Di water doesn't give good results from most pH meters, besides it's pointless... tap and most well water will have a certain amount of mineral (CaCO3 mainly) hardness in it,.. I gather yours is very hard! (more on that in a moment)... CaCO3, or specifically, the carbonate (-CO3) part is what's involved with pH buffering in water; RO/Di has none in it anymore, so even tiny inputs can cause wild swings in pH! That's why , in part, you got a crazy reading like 4.0,... the rest is the meter being out of calibration, which you've addressed, IF the meter is still okay,.. they are sensitive devices, and can be easily messed up by improper storage (not using the right solution), drying out, and being dirty,...
- most alarming here is the water softener! This is an ion-exchange type, using course salt, right? I assume it's NaCl type salt, not Potassium? here's the problem: to remove the hardness(CaCO3), the system uses a type of resin bead that attracts the CaCO3 to it's surface; this has a limited capacity, and to recharge it, it uses a highly saline solution to strip it off the beads,.. what happens is under such high concentration, the Na+ temporarily boots the CaCO3 off, and binds in it's place,... when it goes back to reg. water, this is reversed; the Na get booted off in favor of the CaCO3,... Now the problem: Na is toxic at low levels! It will interfere with other ion uptake, and will become toxic to the plant eventually,... You must stop using it right away, and change sources,...
--- looking at your symptoms, it looks like mostly P defc., but others could be in play,... i don't yet see signs of Na toxicity in the leaves, but that doesn't mean it's not f'ing with things! Now for this situation getting an accurate pH is critical because we need to determine if this is a simple lack-of type deficiency, or an off-pH lockout, and/or a toxicity issue! I'm guessing the latter,... with no reliable soil pH reading, the only option is to flush with more pure water, starting with 3x the pot volume... If RO or Di , low-to-no ppm's water, it should have a small dose of Ca-Mg in it, and pH checked (about 7.0) because straight dope RO/Di will be osmotically harsh on the roots,... In the last pour through, 1/4 str. nutes should be added back in to restore some of the good stuff that has been stripped away along with the bad salts, etc.,...
OK, it's wait and see time for a few days,... Another option for water is those self-fill machines at the grocery stores; they give very low ppm water, at a much better price,...
