34cygni:
Good job at connecting the dots.
My particles are not calcium based. I proved that with vinegar.
Given the amounts of them, dino related is all I can think of at the moment.
Here are the calcium based ones I found on my overflow sides recently.
Foraminifera
I measured my calcium at 400 yesterday and that is the highest for a very long time without adding chemicals on top to my calcium reactor and kalkwasser.
The frequent siphoning could have produced this result.