Another possible Phosphorus deficiency?

Hi all, hope you can help. I've read and read for a week till my head hurts and I think I have a good idea what the problem is, but not positive so thought I'd get your thoughts. My leaves start turning brown at around week 7 and continue to get worse till week 12 when some are totally brown and burnt looking. I thought it might be nute burn so lowered the nutes for a few weeks but that didn't help. I now feel it is a Phosphorous defiency so I've upped the nutes and added additional Cha Ching(9-50-10) and Tiger bloom(2-8-4) which is extra high in phosphorous along with normal amount of Grow big Hydro (3-2-6), but it's only been a few days so no results yet. I also started my room on co2 supplementation with compressed co2, monitored with a simple co2 measuring kit, so I am running about 25% higher nutes now.

I'll post my grow description below.

How long has this problem been going on? A few months.
Are you growing in a PVC grow tent? Growing in a large spare room, 16' x 13' x 10' high. Insulated, heated and cooled.
What system are you running? Home made Ebb & flow with 3 separate reservoirs, air bubblers, stirring pumps, on timers
What STRAIN are you growing?AK48, White Castle, Jock Horror
What was the establishing technique? From Clones
What is the age of your plants? Problems seem to start around week 7 (moved to flowering at week 5) and gets worse until harvested
How tall are the plants? starts when they are about 16" tall
What substrate/medium are you using? Rockwool, 4" cubes, moved to 8" baskets and surrounded by hydroton at week 6, (still in 4" cubes)
What is the Water temperature? 60-72 F
What color are your roots? White & seem to be healthy
What Nutrient's are you using?Fox Farms hydro version. We use all nutes they recommend on their chart, including micro nutes
How much of each nutrient are you using with how much water? We were following their chart precisely when problems started. We change nutes according to their schedule and flush when they say
How often are you feeding? We were watering every 5 hours, but as plants get bigger we water every 4 hours, for 15 minutes. Drains in 10 minutes

What order are you mixing your nutrients? We mix all nutes together in about 1/2 gallon of water, then add to tank
What is the TDS/EC/PPM you are using? Current plants are in week 9 and at about 2200ppm now. Was at 1600 before upping the nutes.
What is the pH of the "Tank"? 5.8 - 6.3, we shoot for the lower side.
Are you sure your calibration is correct on your equiptment? We calibrate several times a week, both PH and PPM meter
How often do you clean your system: example: Flush out water replace with clean water and nutrients? Every 1-2 weeks, according to the Fox Farms schedule
What size bulb are you using? 600 watt, adjust a wings, with super spreaders to keep cool.
What is the distance to the canopy? 18-24"
What is your RH Factor(Relative Humidity)? We keep flowering humidity at 50 - 70%, controlled with de-humidifier
What is the canopy temperature? 64 F nights, up to 85 daytime, with co2
What is the current Air Flow? we have 3 oscillating fans on 60 SF of plant area, with 1 overhead ceiling fan also.
Tell us about your ventilation, intake exhaust and when its running and not running ? We currently keep room sealed and control temps with air conditioning, humidity with De-humidifier and add co2 to keep at about 1200ppm. We run a 450 cfm fan though a carbon filter to scrub the air and keep odors down and mustiness in check.
Is the fan blowing directly at plants? Yes, but they oscillate and bigger fans are 6ft away. Smaller fan is closer
What water are you using? Reverse Osmosis
Are you using water from a water softener? No
Have any pest chemicals been used? If so, What and When? No, we have no pests so far

I should mention that although plants look like hell, they still produce very nice bud with great aroma and potency. Our medical mmj patients love it. But I know this problem is costing yield and probably some quality.

Here's some photos showing the progression.

Your TDS seems high.
What kind of meter do you have?
is it the .5 or .7 conversion?
my ppm during week 6 of flower is around 850ppm on a .5 conversion.
that is 1190 on a .7 conversion.

I have never even gone to 1600.
You might take into consideration once again that your TDS is too high. Get another opinion though.

are you using cal-mag?

I have read that flushing every nute change is a good habit and it has not let me down. If the plant has been burned, like yours, if that's what it is, i use Clear-x in the water. otherwise pure water is fine. the worse the plant the more water up to recommended 2 1/5 times the pot size. let them dry out a little between waterings. I use ebb and grow buckets, fill and drain and always keep my nutes lower than 1100-1200, then taper off on week 7.
pic one 4-6, pic 2 4-14. pic 3 5 weeks into flower and this is the first trim on my worst plant since switching to 12/12. Flush, it can never hurt:thumbsup:

add micro to your reservior first, it may not be getting dilluted enough in 1/2g of water. then your other nutes AFTER the micro has mixed thoroughly.
I'ld never go above 1800ppm for a very hardy plant.

don't forget the cal-mag, since your water is RO
I would feed my plants about half of what you feed