What coolant or additives should be used?

[Daymin]

As part of a GPU upgrade, I will change my loop a bit and will replace the existing coolant.
TLDR: What is the current best practice for coolant/additives?

 

Some information on my loop:

• EK-Supremacy Evo Nickel/Acryl (5 Years old)
• EK-FC1080 Nickel/Acryl (4 Years old)

• EK-CoolStream CLASSIC SE 240 (Copper alloy tubing, Brass chambers)

• EK-CoolStream CE 280 (Copper alloy tubing, Brass chambers)

• Alphacool VPP655PWM + D5 Black Acetal Top

• Mix of old EK and Alphacool brass fittings.
• aqua computer Double Protect Ultra coolant

Because it's a small-factor build I do not have a permanent reservoir and only attach one while filling and bleeding the loop.

(My pump is already mounted to the back of the case because there is no space inside)

I do live in Germany so the minimum would be distilled water as the mineral content of the water here locally is way too high.
But should I add additives to the loop or use some coolant?

I do not want any colour, particles or whatnot as the tubing is black and I don't see any of the insides anyway.

[jaslion]

Basically any CLEAR coolant (clear dyed is ok NOTHING opaque I know you're not doing it just in general statement)

 

Then just make sure it has a anti corrosive and biocide in it. Else nothing more is needed. You can mix em yourself with distilled water, anti corrosive and biocide or buy off the shelf.

 

Also if its been a while id use this time to repaste the cpu too.

[Daymin]

16 minutes ago, jaslion said:

Then just make sure it has a anti corrosive and biocide in it.

Are there any brands that are recommendable? They all seem unreasonably expensive for a simple corrosion inhibitor and a biocide. (Especially because coolants like EKWB CryoFuel don't even include a biocide.

[jaslion]

2 minutes ago, Daymin said:

Are there any brands that are recommendable? They all seem unreasonably expensive for a simple corrosion inhibitor and a biocide. (Especially because coolants like EKWB CryoFuel don't even include a biocide.

I just use alphacools cheapest stuff that ticks the boxes