Chunks in my coolant

Distilled water is all I use, don't want to take any chances. I just did a "light" coolant flush on my Duster (drain and refill radiator) and after 3 years it all still looked good, no signs of corrosion. I use regular green antifreeze concentrate + distilled water + Water Wetter additive and the engine is a 5.9L Magnum with aluminum heads, intake, t-stat housing and radiator. I also made sure there were solid grounds going from the engine to chassis both off one of the heads as well as the block when I swapped the current engine in.

When I first got my '72 D200 pickup the original radiator had what looked like salt crystals stuck all over the inside of the top tank, similar to the chunks in your pics but smaller. Never did cool all that well and eventually sprung a leak so I replaced it with an aluminum rad from ECP as well. Might even be the same model radiator as in my Duster lol. Works damn good too, towed my Duster on a U-haul trailer in 95-degree heat up and down the steep grades of I-25 and it never got over about 210 (has 195 degree thermostat).