White flakes in Water

Hi, new to the hobby.

I've had this tank up for about two months. I do a water change once a week and clean the gravel as well. When I pour in the new water the tank fills with white flakey particulates, which settle after an hour or two.

The tube leading to the sponge filter has this flake build up. Some of the artificial plants do as well but nearly as badly. Can anyone identify the cause?

Thanks in advance.

Pic:

Update: This is what the tank looks like after the water is disturbed.