White Widow Auto - Double the Trouble

Not a lot of pictures this week. I can't figure out how to save plant 6 and I'm afraid plant 7 is next. I flushed them both down to about 400ppm run off and then gave them ample bloom nutrients on top of a regular feeding (-micro for 7) and everything is getting worse. My next step is to get a new pH pen. Even when I calibrate it before every use now it's still telling me to use a lot less pH down than it used to with the same nutrients. In my first grow I used 30 to 40 drops of pH down per gallon of water to get to ~6.5 pH and now I'm using 10-15 drops per gallon of water to get the same results. It doesn't seem like (carbon filtered) tap water should change that much. I'm also going to try using a bloom booster as a last ditch effort to save 6 and 7. They really might not make it another week. Edit: I was using Armor Si last grow which is supposedly highly alkaline which could explain the disparity. From the signs I'm seeing now, it seems like I might kill 2, 6, and 7 before they ever make it to harvest with my feeding/watering/environment. They're also the tallest plants. In my first grow the really tall plant also died from unknown reasons around day 65 or 70. These plants are definitely going to die before that if they do. I wish I had more experience growing other strains to know whether this is a result of weak genetics or something that I'm doing. I'm leaning towards the latter but it's frustrating as hell when you do everything you're "supposed to do" according to everything you read and things just keep getting worse. I turned the light down so there's 600 PPFD at the canopy and plant 2 seems to be doing a little bit better with that. It's less light than I'd like to be giving them but I feel like plant 2 could easily produce a quarter pound on its own if it makes it to harvest. I put plant 3 up on a small milk crate so it's not totally neglected seeing that it's only about 10 inches tall. This grow has me really frustrated at this point and I'm hoping things turn around. I'm truly expecting a smaller harvest from 7 plants than what I got last time from 3 plants. On the bright side, plant 4 is growing like a champ and looks like it could produce 5+ ounces on its own which would make the entire grow worth it. I also wanted to mention that all plants that are producing trichomes at this point smell like you expect White Widow to smell like, except for a single plant that has a very mild version of the cheese pheno from last grow. It's almost more diesel than cheese. More pictures next week. Update: I wanted to add that I did some reading about humic acid and mycorrhizae and now I'm wondering if the issues I'm seeing on 6 and maybe 7 are potentially being caused by an excess of iron. The microbe product I use, Recharge, has humic acid and mycorrhizae which greatly increase the uptake of calcium, magnesium, and iron. Excess iron blocks phosphorous. The problem I'm seeing on 6 and 7 seems to be a phosphorous issue. I used Recharge for every watering for the first ~4 weeks. I'm going to try to really increase the pH of plant 6 to as close to 7.0 as I can to slow the uptake of iron and see what happens from there.