7900 XTX Aqua state

It looks like either algae or corrosion, I am leaning toward algae given I
don't see any green and the fins are copper (dead algae is brown). I would look into
flushing your loop and treating it for microbials and corrosive elements. There
are plenty of guides out there on how to do it. It's pretty common and falls under
maintenance when water cooling with a custom loop. It's one of the reasons I don't
do custom loops anymore, they require maintenance where closed loop and air typically
don't.

By the look of the pic you have caught it before any damage has been done. Corrosion
typically happens when you have mixed metals in your loop, copper + aluminum
maybe some nickel from fittings etc. Algae tends to happen if you don't have
any antimicrobial formula in your cooling liquid. In my experience evidence of
algae is typically only green when the system has been out of use for a while
and water temps haven't killed it. It will be green in the cooler parts of your
loop, like inside the radiator above the water level where it's still humid but
not hot or in your reservoir.

Check your reservoir for any residue at and above the water line.

Either way, all you need is some maintenance from what I can see. Search youtube,
there are some great guides by people far more knowledgeable than me on the subject.

Edited by Xaltar - 19 hours 49 minutes ago at 6:39am

Greetings, been four months since I've purchased 7900 xtx Aqua. My loop includes 5950x with Alphacool waterblock and 2 360 radiators (one 30 mm and one 45 mm) an eisball reservoir/pump combo. And this is how the fins on Aqua look like now: