When I removed my winter cover I found, as expected, green algae. My initial water test results were
FC = 0
pH = 7.2
TA = 70
CYA = 0
I decided last night to purchase CYA so that I could add some in the morning. I hit the pool hard with bleach last night starting at 5:00 pm. While I knew that I needed to add CYA I was pleased to be able to start the process without CYA since the Cl would be more effective without CYA.
After adding more bleach this morning my water test results are
FC = 14.5
CC = 0
pH = 7.2
However, this is a very overcast day. There are very dense clouds and no distinct shadows. If the sun were out most of the pool would be in the shade now due to nearby trees.
My question is the following: Is it the visible light that burns off Cl or ultraviolet light? Do you need CYA when the pool is in the shade or when there is heavy cloud cover? Specifically, if it remains overcast am I better off to add CYA or to shock without CYA until the sun comes out?