Small Black Particles in Radiator Tank Fluid

I recently drained and refilled my coolant/anti-freeze. Everything went smoothly (didn’t spill anything/drain cock plugged back in/radiator cap on okay/ etc). The only problem is that I found small black particles in both the radiator fluid and the fluid in the coolant reservoir tank. The particles are tiny and black (a bit flaky). I found the small black particles in the radiator fluid and the fluid in the coolant reservoir tank after I flushed the coolant and refilled it. To be fair, I don’t know if the small black particles were in the radiator/coolant reservoir tank fluid(s) before the flush.

What is this stuff? Most of the coolant/water mixture is the color of the original coolant/water in the bottle.

Is it rust?

Also, my coolant reservoir tank is moderately dirty. I cleaned most of it when the tank was empty. I used paper towels and wiped the inside and outside of the tank. The bottom of the tank is too difficult to reach (big hands/small opening) and I cannot clean it with paper towels.

Probably a coolant hose starting to disintegrate. What year is the car and when did you last do a hose change ?

If the car and or hoses are greater than 5 years old change them all. I change mine every 3 years as a general rule.

It’s a 1998 Honda Civic DX. I bought the car 2.5 years ago with 126,000 miles on it. It now has 168,000 miles on it. I have not changed the hoses since I bought it. Thanks for the help!

The strange thing would have been if you had not found something in the fluid.

Really? How come?