Mary, the reason we tell you to put the Cya in a sock and leave it in the skimmer, is so it doesn't get backwashed out. Technically it's usually fine to just pour it in, but you will have to backwash before it all dissolves. In your Case, fill one or two socks with the five pounds. Double check that amount. Most cans are 4lb or 8 lb. I don't know that brand, so it may be five lb new. 4-5 pounds will be just about right. Once it's in the sock(s) and in the skimmer, assume it's in the pool. Give the socks a vigorous squeezing often.
Next, it's time to add bleach, and shoot for 16 PPM FC. It's so close, let's add (3) 121oz jugs of 8.25%. That will bump you a little over 16, which will drop pretty quickly on the front end of this procedure. From here, your job is to test FC, and use Pool Math to raise it back to 16 from wherever you catch it. It will fall back down, and you want this to happen as little as possible. After your first bleach addition, give it about a few hours and re test FC. You'll soon get a feel for how fast it's dropping and that will give you a better idea of how often you need to be testing. You won't have to continue every few hours testing as a rigid timline until done, but at first you want to get a feel for how long your additions are lasting. Have you tried out Pool Match yet? It's easy, but if you need some pointers, just ask. Or ask about anything else before you start if need be.
From here, and once all the above is done, do not test for pH, or Cya. They will be fine.
