Polytunnel Grow Soil PH different at different depths - help!

Heyup folks ..have been a lurker for grow tips for a couple of years, this is my virgin post!

I grow in a polytunnel.

I'm worried about the PH.
I've tested the first 5 inches of soil - it's between 6.4-6.8
Deeper soil around 8-10 inches - 6.2

My water is from a natural spring and it's a shocking 5.5!! It has loads of lime in it which scales up my kettle in just a few days so i have no idea why i get such an acidic reading. A urine test strip reading of PH gave me 6.5 but my soil meter tested it at 5.5.

(I've just ordered a digital PH meter...not sure i trust my current meter..)

Plants are showing signs of nutrient lock-out (upper leaves starting to fade, despite feeding) , and when i fed them last within 2 days only the 2 lower fan leaves started to look burnt, brown and crispy around the edges.
This is my 3rd grow. Learning all the time.

SO - I need to bring PH up. As every time i water i'm making it more acidic. (NOW i know!)
I added hydrated lime to water and the PH went crazy high...way above 10. So i diluted it down to get a P.H of 8.
Gave each plant about a litre each. Large plants so not much added in case i was f*cking up!
Soil already moist from last watering (crappy weather)

Did i overdo it with the P.H 8 lime water? Will it fry the roots? I'm kinda concerned i've just done the worst thing....but i need to raise the PH of the deeper soil to encourage deeper root growth. I see the roots growing out the sides of the mounds instead of down...due to PH i think.

Should i keep adding the 8 ph water that will eventually soak down to the deeper more acidic soil?

I will have to wait a day to add anymore liquid to flush the soil if i need to as they're already wet enough and will seriously droop! (shitty weather! I'm in the northern hem.)

Hope someone can chip in with some experience of this....cheers in advance for your help!

You can try mixing dolomite lime in with your soil for next time. I would flush with 6.2 water thoroughly and then let dry out real good and add some dolomite lime as a slight top dress the soil. This is all theory though for me as I do hydro so I don't have to worry about the complications in ph that soil brings

Thanks for the suggestion Neo,
I was reading about dolomite lime and most rekon it takes a good few months to work through the soil to change PH...hydrated lime is advised for 'instant' PH changes.
I will lime thoroughly and deep for the next grow, months before planting out.
I'll monitor the girls through the next few days..hopefully i haven't done too much damage!