root rot need a way to cool my nute mix in dwc bucket

what are my options for cooling my nutrient mix in my dwc bucket. dont know the actual temp but when i went to check my ph it felt warmer than average room temp. and im noticing what looks like root rot or browning of my upper roots. the plant itself hasent slowed growth at all and is still looking very lush and green id like to fix this before it turns into anything worse

need pic of your setup to better help

they sell chillers, but they are a couple hundred bucks from hydro stores.. and i've seen on here a diy on how to use a mini fridge to cool your res, which looks like an awesome option.. lemme know if you'd like to see the thread, and i'll see if i can locate it for you..

In my cooler I drop 1/2gal frozen water bottles with 2 - 0.5lb fishing weights in them to hold them down and in place with all that bubble action goin on.
I replace them every 24hrs.
Temps stay low to mid 60's too.

yes.
frozen bottles.
flo got it again.
lol!