Pool problems.

[Watermom]

You are correct. You take the reading when you can no longer see the dot. So, we'll assume that your cya is 70. With a cya that high, you'll have to run higher than normal chlorine levels to kill algae and subsequently to keep it from coming back once it is gone. Take a look at the chart at the following link. You need to shock to 20ppm and try and hold it there to clear your pool. Test 3x a day and each time, add enough bleach to raise it back up to 20. After the algae is gone, you'll need to maintain your chlorine levels between 5-10 all the time. In a 20,000 gallon pool, every 2 quarts (half gallon) of 6% bleach will raise your chlorine level by about 1.5ppm.

I really think you should consider buying Ben's testkit at the www.poolsolutions.com website especially since it will allow you to test high chlorine levels which you are going to need with high cya. Most other kits you can buy can only test up to about 5. Well worth the money and what most of us use. Another option you have after you clear your pool is to do a partial drain and lower your cya. If you replace half your water, that would put your cya at about 35 which would be good. But, that is a lot of water to replace. You may just decide to live with the high cya.

Hang in there and keep hitting it with bleach. We'll stay with you until you get your problem taken care of.

http://www.poolforum.com/pf2/showthread.php?t=365