I tried those probes in the past with the 2 metal prongs. They don't work. They're only good to test the moisture of the medium and it's not even accurate at that. Def need a better pH pen. Apera had the PH20 for like 50$. It's not that expensive and mine has been running strong for over a year.
The issue is that peat is acidic..... Bottled nutes are acidic. You need some dolomite lime, at least, when mixing the soil. It's a problem I was running into for years before I figured out the problem. I was growing in peat and I would have pH of 4.5 once I started adding ag lime, gypsum and dolomite lime to my soil mix that the problems went away.
At this point, maybe best thing to do is top dress with some ag lime or dolomite lime. It will help with the peat acidity. As far as the nutes go, I would mix them as normal. Keep the pH like 6.5ish. It should hopefully balance out. The extra calcium shouldn't be an issue since they love calcium.
For quick fix you can def foliar spray to keep the plant happy but you def need to address the peat acidity. I think peat is like 4.0ph. Maybe in the future of you're going to use liquid nutrients, maybe go with Coco. It's neutral in pH, you can also add the calcium in the beginning and you won't have any nutrient leeching. Or get nutrients designed for peat like TPS has I believe.