Edge70

Hi there , hoping someone can help. I drained our tub the other day and changed the water. Water appeared to be ok but it needed to be changed. A few days after changing it the water looks like this. I’ve had this off and on for a year now but this time seems to be the worst. How can I get rid of this?? I’ve tried to purge with things like swirl away and awesome but nothing seems to work. I’ve changes the water a lot but it still seems to be a problem. Please help. Thank you for advice.