水草情迷

my tank has many little worm (1-2mm), white in color, center is black, circle in size
worm...... what is it??
how to clear????
they usually appear after switching on the light for few minutes......pls help!!

It may come from the iron rust of your tap.
When I was a kid and cleaned the bathroom (forced by my old mom of course), I found them at the rust around the tap.
They are disgusting.