Pool Water Has Stayed below 50F. Why Algae Now?

[FNG]

I work from home and pool is open so I can always keep an eye on it. These green spots just randomly started to appear today. There's about 20 of them. Water temp is 49F now and has been around 40 for several weeks. I haven't run Chlorine at all during the Winter since water is cold. And I did do a Winter algae prevention and winter shock back in October. Why would Algae form now?


I went ahead and put Chlorine in this morning because I know that won't hurt but I'm not understanding why this would happen.

 

[Texas Splash]

Why would Algae form now?

Cold water slows down organic growth, but doesn't eliminate it completely. We still need to maintain the proper FC level as noted on the FC/CYA Levels. Now that you have confirmed the presence of algae, it's time to start a SLAM Process to get rid of it properly. Good thing is with chilly water the SLAM should go rather efficiently if you follow that page closely.

 

[Mdragger88]

Lack of free chlorine is the reason as Pat mentioned, gotta keep fc above minimum for your cya at all times
FC/CYA Levels.

It’s
SLAM Process time now to eradicate the algae.
Be sure to remove any steps/ladders aka algae hotels & scrub them inside & out during the process.
You will need a proper test kit to do the slam
Test Kits Compared
if you already have one,
add which one it is to your signature so everyone knows what you’re working with.

 

[FNG]

Thank you for the responses.