Leaf canoeing and brown spots

Hello all, let me start by saying this is my first grow. I have 3 Vortex clones growing in their own 5gal DWC buckets. I have one 600w hps light. All plants are receiving Technaflora recipe for success starter kit.

The light is about 15" away from my closest top. Temps are about 68-72F and humidity is 30-45%. Steady.

The plants are at day 40 of 50-55 day flowering.

Last week my nutes got a little out of control, and had too strong of a solution. Around 2500 ppm. PH was off as well. I thought that the leaves browning was due to the high concentration of nutes.

I flushed for 24 hrs with PH tap water. The browning seemed to go away a bit, but now, about 5 days later it looks a little worse/not better.

The canoeing leaves I thought were normal, but with browning I thought I should look into it a bit more. It seems to be worse on my colas, and traveling down. Only goes about a 3rd of the way down, then normal leaves. Any thoughts?

I only have about 15 days max, so wondering if flushing for the rest of those days would be best, or if I would loose out on a lot of bud mass.

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