I’m in Florida so the issue is actually heat in the garage :/ but okay I’ve been keeping the water moving I won’t be doing that anymore. The only issue I had with the brown stuff is actually having to clean the vat so oftenCorrect.
Mix until it's done and then stop. This can take as little as five minutes, usually no more than 15 minutes.
If the water gets too cold to use in your garage, just make sure you are heating it minimally. I used to store my water in the basement on the floor so it would always trend toward earth temperatures… 65 to 70°. I never had a problem with it at that temperature. Just for example.
Depending on your situation, I would even try heating it right before you use it versus heating the vat and keeping it warm all the time.

...or if you do, it's just for aesthetics. (ie not something to worry about)
Well I guess I'm good then
Ill keep heating and mixing.
These are two ATI ICP result from RODI pulled from the same container at the same time but sent in separately with two display water samples.