First DWC hydro grow w/ minor burns.

Hello
I started my first ever hydro grow two weeks ago.
I am running 5 gallon buckets in DWC.

I misunderstood the Lucas formula and don't remember or know what I gave these seedlings the first week.
Now for the 2nd week I am using GH Flora series: 5ml Micro, 10ml Bloom per gallon at 25% strength.
They are at 315PPM. PH 5.7-6.2. PH downed 1-2 times a day. Using Hard water (tap is at: 60-70ppm).

My Super Skunk has a lot burns on it's leafs.
Should I still flush her ( and how?). Or since the nutes are correct now( I think), just let her grow and let her start using all the nutes that might be stuck in the medium or what not.

Here's pics of the Super Skunk:

Any help is appreciated.

Also does anyone know an easy way to cool the water in your DWC set up?
I am afraid of getting root rot since the water in my buckets is around 85'F...
Help!