There are basically three reasons you might see flakes in your spa water. The first, and most likely, is calcium scaling. Generally, this won’t appear as flakes floating in your water, but it can.
The second is biofilm. Again, this doesn’t usually appear as flakes in your spa water, but it can under certain conditions. More on this below.
The third is white water mold. Though not uncommon in pools, white water mold is quite rare in a hot tub, but it can occur.
