So flush them with phd ro water
Then 1/4th strength nutes?
NEVER use the makers nute charts for other than guidance. I use AN and if I followed their chart I'd burn my plants to the ground! They want you to use 4ml/L of everything from sprout to week 7. Then if you're adding all the supplements they sell it's a race to see if the plants all die before your bank account closes for lack of funds.
I rarely feed my soilless plants more than half at 2ml/L unless they indicate to me that that's not enough and they get just RO water with a dash of CalMag between feedings.
Of their stuff I only use the 3-part base nutes that cost the same as GH at any stores I've shopped at. I got gallon jugs of each for $40 a pop so they aren't more expensive than any other. It's the supplements they suck rookies into buying that cost an arm and a leg. I also get their Rhino Skin for the silica and Big Bud for a bloom booster and love that stuff. Got a 500g can of the powder for $80 and that will last for 5 years. The liquid goes bad in a year. They make it in an organic version now too along with some of their other stuff. 17 years now and don't have any complaints. Any old CalMag will do and some epsom salts once in a while.
There is no need to pH RO water. It's neutral and has no pH of it's own until you add something to it. Same with distilled water. Always mix your nutes first then adjust your pH if you feel the need. If those are organic nutes they won't read correctly and it's best to just water them in without messing with the pH. Something's got to be wrong for you to get pH 3.5 after mixing up your nutes. Botanicare is owned by Scott's Miracle-Gro now so who knows what they are doing with that line. Nothing good I suspect.
I'd give them a flush about the same volume your pots. Get it soaked to the point of runoff and let them sit for at least an hour to let the salts mix in good then slowly pour thru the same volume of water as the pot holds. That should reduce the excess salts plenty enough to see you thru to the end now. Try to add it evenly across the surface so you basically have a wall of clean water pushing the salty stuff out the bottom. I used a shop
You can't get rid of the salts already built up in the plant tissues but you can prevent it from getting worse by flushing what you can from the root zone. There will be more than enough mobile nutes stored up for the plant to steal what it needs to finish. With any luck you'll see the buds swell up good the last couple weeks before harvest.
By the end of week 6 of an 8-9 week strain you should just be watering without food. A little bit of CalMag or better yet Epsom salts for the added sulfur which is the 'secret' ingredient in bloom boosters to make more resin but not much else unless you're getting a lot of yellowing with soft, supple leaves. Not the hard, crispy ones yet to come but soft and yellow indicating the plant is stealing nutes from them to keep the buds going.
Good luck!