Liquid Cooling Suggestions
We tested our liquid-cooled hotends with Koolance's RPM-ALX400 (https://koolance.com/reservoir-pump-module-rpm-alx400), but it provides way more cooling than is necessary. The smallest pumps available for cooling computers, for example, provide an order of magnitude more flow than is needed. If using a pump for cooling computers, you will most likely need G1/4 to G1/8 adapters. An example of one can be found here (https://www.mcmaster.com/9491N13/).
Concerning the coolant, we recommend an engineered coolant with biological inhibitors that does not void the warranty of the cooling system. The coolant we use in-house is Koolance 705. Since it is a electrical insulate, it is less of a potential problem around electronics if a leak occurs. The cooling system should not contain aluminum parts unless those parts are coated with nickel.