Unable to get radiator completely clean
I have a Hardware Labs 360 GTS radiator that I've been trying to clean and install in my loop but I'm have a lot of trouble getting it fully clean.
I used Mayhems Blitz Part 1 for the initial cleaning and I'm currently trying to flush everything. For each flush I filled the radiator half-way with distilled water and shook it vigorously side-to-side and up and down for about 30 seconds.
I've attached an image of what the flushed contents look like after about 20-30 flushes. No matter what I've tried so far these brown "flakes" still come out of the radiator in roughly the same amounts each flush.
I even tried hooking up the radiator to my faucet, running some hot water for 10 minutes, and then doing an additional 10 flushes with distilled water and it's still the same thing.
Is this some kind of corrosion in the radiator or do I just need to keep going? I've quite literally spent 2-3 hours and about 2 gallons of distilled water trying to get this thing completely clean and I see no end in sight.