Oxyclean grit

[Derp]

I usually fill a large Rubbermaid container with water and Oxyclean when I clean my kegs and brewing equipment. I've never had a problem with leaving stuff to soak overnight but over the last few weeks I've had a problem with a gritty residue. It removes easily enough in a Starsan soak but I don't know why this problem has just appeared. It's been cold outside, does Oxyclean precipitate at lower temperatures?

 

[samc]

Oxy works best when added to hot water. Otherwise it does not dissolve very well.