My thoughts, in my grow (ratios considered), 100ppm of nitrate was toxic by mid bloom, but that's with my K at 200 and P at 65. This PC is at day 26, is under developed, but I stuffed her in there at 6 weeks old which is very young in my grow. Her leaves are very dark green and that is the result of too much nitrate, so I'm heading back down to 95ppm with my NO3 and bringing my K back down as well.
Back to the P topic, 25ppm is much closer in range to other brands, as well as Hoagland and Steiner's. I started off deficient at 50 so I went north. My petioles resemble half green apples so I'm confident I'm close to ideal at 70ppm, otherwise they stay red at 65 and lower.
I'm glad I got to see your regimen. I've never seen another Megacrop user give half a fuck to dress up the brand with other products like you're doing. You did well to reign in the contents and got them much closer to ideal. What I dislike most about all brands is the difficulty it is to change the ratios. It's like you'll always need to accept that you can't change certain things if you want to, especially in the micros. Ever since I mixed my own micro blend, I hit all of my macro targets perfectly only taking errors to sulfur, but in a good way, lol.
IMO, 100-50-150-100-50 (N-P-K-Ca-Mg) is a great starting point for hydro, rock wool at least.
Edit - the pic is the product of 3 weeks of
N - 100
P - 60
K - 180
Ca - 120
Mg - 75
S - 138 (targeted to 100)
Edit#2 - the above is my "stretch" regimen, 3rd revised high brix attempt. Next res I'm doing my 4th revised that will be less N, more P and less Mg