What was your reservoir made out of (metal?) and was the kill coil sitting in contact with it?
No the reservoir was an EK pump and it was plastic, not sure about base and cap actually - in skip now
What was your reservoir made out of (metal?) and was the kill coil sitting in contact with it?
. Sure you didn’t buy a bottle of seawater by mistake? 

What make was the Radiator ?
All the other fittings look OK from the photo, maybe an aluminium radiator ?
The GPU block looks 'rusty' could be the nickel plating flaking into the loop and showing the bare copper beneath.
As others have said, a visual check every few months would have prevented this, but hindsight and all that
Hope damage is kept to a minimum.
That post is 8 years old, is probably due an update. I think nickel plated blocks especially are relatively new. EK had a lot of problems with nickel flaking in early revisions, there was drama.
Silver works as biocide.I set up my own loop for the first time this year and read about things like sikver coils as I'd seen others use them, but from what I found it's best not to use them!
Yeah, I'm suspicious that if the coil was sat in a plastic reservoir, then it's likely to be something else. Only time I've seen corrosion is between brass fittings and copper radiators.Silver works as biocide.
But electrically it's just another risk factor for galvanic corrosion being more "noble" metal than copper or brass, or especially aluminium.
https://martinsliquidlab.wordpress.com/2012/01/24/corrosion-explored/
Air for life!


What pc did you have loop problems with last year in this thread?
The way a silver coil works as a biocide is by releasing silver ions into the fluid. (probably by oxidising as silver oxide is highly soluble in water) Because of that, it will always cause corrosion in loops which contain other metals and no corrosion inhibitor.
A good fluid with inhibitors can work fine for years. The barb on the left has only seen one fluid change in 2017 and has been in near constant use for nearly 7 years. Still has all it's nickel plating intact on the inside. (PTFE tape and o ring were a bit knackered so I replaced them)