Nutrient PH too low

Merry Christmas! Can anyone help with this? I’ve been mixing nutrients in 5 gallon buckets of water for a month. It’s a lot of work for 36 plants so I bought a 35 gallon tank and we just started mixing in there. RO water fills the tank and ph = 6.5. Then I start adding my nutes. Soil A and ph slightly drops. Soil B and PH drop dramatically to like 3.8 add multi zen, root excellerator and drip clean and my batch is testing at 3.6.
I thought I was going crazy so I mixed a new batch in the 5 gallon bucket and ph = 5.6. Mixed a small cup and ph = 5.6. I poured the 35 gallon mix down the drain, started over and got the same 3.4 what the hell???

Can I use pH up to get it to 6.5? I heard that that causes too many ppm’s. What’s going to happen if I put this mix on my plants?

I have the same problem. I collect rain water and its ph is around 6.1-5. After adding nutrients it gets to the low 5s. I add general hydroponics ph up and it doesn’t mess with my tds at all

Yes, pH UP and pH DOWN are used for that exact purpose, to correct the pH of the water or the nutrient solution.