Any recommendations on a biocide for the cooling water? Kinda afraid to just use bleach because I don’t want to corrode the inside of the spindle.
Deionized-water + antifreeze mix (depends on climate). Use DI or RO water, not tap water.
Mix in fish tank algee control from pet section at local pet store or Walmart.
Then mix in a nice helping of gold “antiseptic” Listerine. I used 1/4 to 1/3 of a bottle in a 5gallon pail.
What if I put a strong UV light in the water tank 
That’s another good idea.