Rockwool Ph Runoff through the roof!

Hey there I'm new to rollitup. For the last week i have been having crazy PH issues, maybe someone here will catch what i seem to be missing.

I am running drip to waste through an Easy Feed Systems Doser.
I have jar tested my mix 24 hours later and ph remained at 5.5
I am running GH 3 part at 500 ppms equal parts of each.
I am using 6" Grodan Hugo Blocks.
PH Down is Earth Juice Granular. I mix 5 gallons at a time with 1 quart per gallon.

Soooo, I presoaked all 160 cubes overnight in 5.5 water. The next Morning cubes were placed into 4x4 low tide drip trays (20 cubes per tray). Next i installed all my drippers and set up the doser to deliver 500 ppms of GH 3 part @ ph 5.5. I then ran the droppers for 3 minutes giving me a couple hundred gallons of runoff that was 5.5-5.6. Everything seemed groovy so i installed all of my clones, which were heavily rooted in 1' rock wool. ph 5.5 and 300ppms of food. I did not water anything for 3 days and then ran the second cycle. Ph and ppms were exactly the same coming from the doser but to my dismay the runoff from the cubes was 7.7-7.8. So i hooked up a hose top my easy feed system and top watered about two gallons per block at a ph of 5.5 and it started to come down to the low 6's in ph. NExt day i checked the runoff back into the mid 7's. SO this time i flooded all the trays at ph 5 for about an hour and the next day the cubes are running off at ph 7.7 again.

What am i missing???? i feel like I'm starting to crazy here. The plants are starting to show signs of ph stress and what may be a bit of calcium lockout, and I'm about one day from pulling the clones from the cubes and buying a pallet of soil.

Any help or ideas will be greatly appreciated

Ok, first off, you might need to take it easy on everything.

I run seedlings and clones in rockwool cubes straight out of the package without even soaking overnight (just add water before hand) and I use nothing for 2 weeks other than a dash of clone gel for clones. Everything gets straight up tap in the cubes and a light misting. I don't care about ph at this point because ph comes into play for nutrient uptake for the most part.

If you want a good medium look at coco, thats what I use. I do cubes at first then transplant to coco (good coco, I never wash that out either or check ph). I never check run off, but I do check when mix new batches and feed.

One thing I heard about rockwool is you can get a fair amount of lime rock sometimes, and will be a constant fight that you can never flush out. I have never had a ph problem with coco and the cubes. Usually I run my water at 6.0 - 5.8 ph -ish when I mix feeds. After that I might have to make tiny adjustments.

One major difference, I do not have a closed loop res. And I think that's where most people get these issues from, regardless of medium. I guess thats the difference between re-using run off (or having a closed loop systems) vs just mixing a new batch and letting run off go down the drain..I never have to fuck with my ph after its been adjusted the first time because its always pristine going in. Another thought is you could do the same run half strength mix twice a week and run to waste or something for same effect. Or try aero with a pvc pipe and a few modifications to your setup and you don't have to worry about any medium tainting your ph. The real thing for having a medium with hydro is just for buffer if something goes wrong and air, nothing more.

How old are clones?

thanks smegpot. the clones first popped roots about 12 days before transplant and were started at 200ppms and slowly raised while they rooted into 6". Also i do not recirculate. I use nutrient injectors and drain to waste, so the ph in the rock wool changes but the input is always the same.

also since transplanting into these 6" blocks, the clones went from healthy and green to having deep dark purple stems and leaves that look like this

To be honest if your plants are not looking stressed I wouldn't worry. Its the lime in the wool dissolving most likely. I have no idea what effect that has without the coco coir as a buffer in your case but i've done decent loads for the past 4 years without giving two hoots what my run off looks like. My tap water is high ph, 8.5+, I do ph that all at once in a 5 gallon tub once a week. It usually climes a few points over a week but not much if I keep the lid on the water res. Not sure if evaporation plays a part, I guess it does.

You could also try foliar spraying until the roots get a little stronger. At least until you figure out what you are going to do. Looks like they are to wet to me. Yellow and Purple = to much water. Let them dry out a bit.