Just distilled water, XSPC dual 5.25" bay res. not too much tubing.
Was just interested, I don't want to go buying some massive 5 litre thing if I only need a couple. The answer can be as vague as my question.
I do not like the coolants with a DYE in them, this may destroy your loop and blocks. If you want color get colored tubing or paint the tubing but do not add DYE To your loop as it will bake to the inside of your blocks causing temps to rise and my clog the loop altogether
Dye is usually a little safer than 'coolants' since the only real addition they typically have is just the dye itself. Coolants tend to have some kind of proprietary concoction of glycol or other mixtures that is said to perform to a specific spec, but 99.99% of those instances are simply the peddling of snake oil.
Coolants should be scrutinized before considering- under constant, high loads some have been seen to break down and precipitate into coagulated matter which collects in CPU blocks and radiators. Feser One Blue mix is one of the most notable offenders, although there are others that have caused the same to happen.
Distilled water is just the best. Toss in some sort of antimicrobial and you are set.
I just buy a gallon of distilled, but depending on where you live in the world, you might find it in liter containers, but even then, you shouldn't need more than 2-3 at very most unless you have a huge reservoir.