Cooling Waterblock Residue Buildup

I have been having my first foray in to water cooling, and after leaving my water loop filled for about a week, I have noticed in the GPU block a greyish build up of something...

I wasn't sure what it was or whether I need to clean it out or what.

I am using RO (Reverse Osmosis) Water, which should have almost nothing in it, and the RO Unit I have has a de-ionisation unit too.

Here are the photos (click for original size)




If anyone has any ideas about what might be causing this i would be very grateful.

 

What else have you got in your loop? It looks a bit like mould.

 

The whole loop description please, thats either mould, corrosion (galvanic) which means there is some aluminium in there or other disimular metal.

If it was my loop it would be iron oxide particles, as i had an M3 bolt on my rad rust, due to the brass one sheering off. (bleed valve) cleaned it out, but still get the odd about appear no and then! rofl!

 

Ah Sorry for missing out that information.

The loop is as follows:

Laing DDC Pump
EK-DDC X-RES
EK-FC4000 GPU Block
EK-Supreme CPU Block
Black Ice GT Xtreme 360 radiator.

Photos of all parts are here if that helps

 

Did you rinse out the rad properly before you put the loop together?

I know you say you have an RO machine (never heard of one before, what an interesting idea), but what did you put the water in to get it into the loop? As Burnout suggests it looks a little bit like either mould, corrosion, or in my eyes, bits of black powdercoat.

 

I hadn't cleaned out the radiator before using it
I will go and do that now.

The RO machine is my dad's he uses it for the water in his fish tank (nothing in the water including spare oxygen, so it has to be bubbled with air first or else fish drown!)

To get the water into the loop it went from a milk bottle (clean, has been used with only RO water for months) via a plastic funnel and a short piece of pipe and a standard G1/4 connector.