Just my experience, this is my first playing with dwc also so just speculations here. I was having some issues with light foam as well, if your solution is heavily aerated it could cause foam slightly, and even depending on the nutes it could foam. I’m in a 35 gallon bucket and when I lose about 5 gallons I start to foam slightly. I would just keep with consistent res changes, especially with that temp, I use a frozen 2L bottle and it takes my temps to 68 from 73f. I also use Hydroguard, they can’t ship to Illinois so I buy from eBay the sellers don’t care. Also wrapping your buckets in reflectixe from Home Depot took my temps from a constant 80 to 72 without ice, just an fyi.