1st grow, leaves turning brown, need help

[Semper Fi]

First grow, wife’s medical MJ. Getting her off Prescription Painkillers. Couldn't grow in the Corps, just retired. AZ Prop 203 passed, she is a card caring member. Not As Easy As I Thought. Researched all sites like 420 MAGAZINE, found this one most informative. Having members on top of their game and willing to help others. Spent hours reading 420's forums, problems similar to mine. Have an idea of info needed, to diagnose problems. Info and pics below. Thanks in advance for any help...

Leafs are curling up and down. They have brown, rust like spots / lines on the leaves. Those are getting brittle to the touch. Thou they continue to grow green up top.

6 plants > 2 Lowryder #2 and 4 White Widow

Put in Turbogarden Aero 9/18, 9/21/ 9/22. All were healthy seedlings with good root structure

About 20 gallon in the reservoir ¼ strength of Botanicare CNS17 ( 3-2-4 ) and Liquid Karma ( .1-.1-.5 )

H2O on 1 min - off 5 min

2 air stones in tank, 12 inches long

Kessil 350 and 150 purple LED Lights 14 inches above plants.

12 inch circulating fan

Room Temp > 70 to 81 degrees

Humidity > 25 to 60

960 PPM last 2 days

H2O out of tap is 7.6 PH - 450 PPM

Using H2O from Botinicare Smallboy De-Chlorinator & Sediment filter. 7.6 PH - 550 PPM
Ruled out RO system, H2O delivered to home at 4 cents a gallon.

Had problems controlling PH for first 5 days. Garden came with Botanicare PH down. Went through a quart in a few days, to get the PH down. Supplier told me, balance H2O first, found out that was wrong. Wife went out of town 9/22 with only car, stores 60 miles away. Ran out of Ph down and started using white vinegar. Worked briefly, than went right back up. Evening of 9/24 it was 5.6 PH and has been there till this morning 9/26. Wife home today with qt of sulfuric acid, going to mix 1 cup with a gallon of distilled H2O.

Had CO2 on first five days, swing to wide. Have to take the time and adjust it. Read somewhere, mainly used in bloom. Air from under home, 6 inch with damper, 6200 feet elevation. Maintains CO2 at about 480 to 660. Exhaust is 340 CFM Duct in-line blower, with carbon filter.

Thats about it. Whats the best way to drain and replenish tank, without shocking plans? Thanks again.