You need to test your CYA in the manner Ben instructed in post #2 (see above). The CYA test is tricky to read at best and levels showing approx. 100 could easily be much much higher. Please let us know when you have done the 1:1 dilution CYA test and what level you get. Reason: If your CYA is much higher than 100, (or even right at 100) you may need to take measures to reduce it. It is quite difficult to maintain high enough chlorine to prevent algae and sanitize in a pool with that much CYA. (Been there myself before finding this forum). You will use ridiculous amounts of bleach to keep a high enough chlorine level (see Ben's Best Guess chart) to be effective in a high CYA pool. But first, most importantly, you must know how much CYA is REALLY there.

I had bloom after bloom after bloom when my CYA got in the 100 range years ago... the pool store man just said to keep shocking! Used dichlor shock! Raised my CYA even more!!! Water turned a beautiful transparent emerald green. Thought it was metals... Wrong! It was just algae. My problem did not go away 'til draining a lot of water to dilute CYA, stopping trichlor pucks, and balancing everything properly with the BBB method. You can fix this... easily, but may take a little time. Everybody here will help.

Let us know what your true CYA level is and folks will be ready to help.