Changing or cleaning the sand is rarely necessary; replacing 'missing' sand is often needed on AG pools with oversized pumps and undersized filters.

I don't recommend any in particular; even known brands change ingredient chemicals regularly. But, I've never known one of those products to make things worse, UNLESS an overdose was applied.

Cloudy,gray water is the typical aftermath of algae; cloudy, greenish often indicates not-quite-dead algae. So keep stepping chlorine levels up, till you arrive at "cloudy, gray". Brushing will help remove and kill algae that's on floors and walls.

Check for air leaks around the pump -- otherwise, leave the bubble issue till later.