Best coolant

Then just use distlilled water and some PTnuke.

Does distilled water cool better than Feser One fluid or other fluids? If I go distilled water is is still non conductive after it hits the rad, pump blocks etc?

Distilled is the best as far as performance. I believe that feser 1 was neck and neck with distilled, but it is also much more expensive. You could most liely get away with 100% distilled and nothing else as copper will act as a mild biocide on its own. I recommend either getting some iandh killcoils (silver coils that kill algae etc.) or some PT nuke to be on the safe side. Either solution will last you a long time.

I use a little pentosin as a UV additive. This helps spot leaks etc. You may also want to add a drop of dish soap to act as a surfactant. This reduces surface tension which make the bubble smaller and can help bleed the loop faster. (I also think this has helped temps a bit, but not much and I am not 100% on that)

100% distilled is non-conductive, but keep in mind, any coolant you use will eventually become conductive as it picks up solvents and ions from the materials in the loop. The best thing to do is leak test thoroughly and prevent the leak in the first place.

Distilled may be just slightly better for temps, but after my loop was together for 4 months and I had a hose crack and feser one went directly into my psu while it was on with no problem except for the mild coronary I had, I will never switch to water....