White substance on pool floor

[dcrolltide]

Hola friends. Been getting this white powdery substance on the floor of my pebble (SWG) pool for a couple weeks now. Also robot vac is scooping it up. Any idea what this could be ? Calcium levels are normal range…

 

[PoolStored]

How are you testing your water chemistry. Can you post a full set of results? FC, CC, pH, TA, CH, CYA.

 

[wireform]

Put a little muratic acid on the white stuff, if it bubbles it's calcium but as @PoolStored above asked what are your testing methods.