Hi all. I've got a couple of Comets in a 10 gallon tank with a standard filter system. For some reason, there's a constant buildup of what looks like limescale in the water and on the inside of the glass. It gradually builds up day by day and completely covers the inside of the tank with a cloudy white coat. There's also loads of little white bits floating around in the water. The filter picks up some of this but it seems like it cant keep up with it.

Is this harmful to my fish?

I think a stronger pump or a second filter might help but I need a quick fix until I can afford to buy them.
I've already lost 3 fish and I don't wanna lose any more...

See the white bits on the surface and stuck on the glass??