This could be pollen depending on the time of year.
turn the water yellow
5284.62 gallons
70
Shock treatment for the green part. If it is still cloudy you can add a clarifier sold at your local pool supply.
5300 Gal
18,000
If 20' is the circumference, then the answer is 833.4 gallons.
'bout 1500 to 2000
Can't say unless you tell us how high the pool is.
6015.77 gallons
There is NO way to calculate this without knowing how deep the pool is filled!
Pool shops have all kinds of cleaner to deal with these types of problems withou upsetting the waters chemical balance.