Clorine Block - Need Advice

[kevinob]

I have a 20,000 gallon vinyl liner in ground pool using a sand filter. About a week ago the water turned green. We have tried multiple applications of algicide. The green color has gone. Now the water is cloudy. We can see the bottom pattern at the shallow end, but not the deep end. Over the past 5 days we have, on the first 4, done repeated 8 pound shock treatments each day. Water is now blue, as indicated above. Numbers are as follows this morning:
the ph was 6.8 alkalinity 140 or 150. Cyan stabilizer was 100. Chlorine was 1 but it measured total chlorine. These measurements were done using a pool kit which did not offer a test for free chlorine. We tested with at strip for FC and it was about .5. The strip was slightly lavender at the edge of the sponge so free chlorine might be .5. It wasn’t completely colorless but close. The whole sponge was lavender the morning after the last 8 pack shock. It was definitely 1 in free chlorine then.

I have a large quantity (about 16 gallons) of 6% Chlorine Bleach availalbe. Question is, how much should I use? Any other ideas?

I forgot to mention - I have a Nature II unit if that makes a difference. Thanks.