Sensi Grow pH Perfect Problems

Hello all and thanks in advance for the help!!

Im 20 days into my first R-drip system using hydroton (thoroughly rinsed and soaked properly) with 9 girls under 2 600 watt lights

My concern is this:
Like so many others, after mixing AN Sensi Grow

at a ratio of .75 ml/L (im starting a couple seeds alongside these fresh clones)

Readings are at 6.8 ph

A bit of background--week one i burned the plants with GH pH down, not having a ppm meter and my water not going below 5.9 i was dumping ph down into the bucket

And since correcting, with my ppm at 550/700 and ph @5.9 my growth is stunted. Im watering 3x daily and im foliar feeding calmag 3x weekly with fulvic acid.

So after reading all the talk on the pH perfect line, im wondering if adjusting the ph with ph down (phosphorus based) if i burned my plants with phosphorus and am seeing the result now.

Anyone here have experience with the Sensi Grow line, in hydroponics, at an unusually high ph level?

Before I started using AN, I did a lot of research on people's experiences with their pH Perfect products. What I found was that the people that always had issues were the people that insisted on checking their pH. I just let it do its thing without checking pH and I've had zero issues

Thats the general trend I'm seeing, just looking for a large amount of varying responses, not only for my own benefit but for anyone else who is having my problems.

So wild that the traditional pH parameters don't apply here!

Hope to hear more from others!
Also, anyone with experience in phosphorus toxicity/deficiency!