Pool water green and water 40 degrees

[Slachey]

We recently had some warm weather here in Eastern PA and I did not check my pool water temp, but over the last 3 weeks my water went from clear to green. My AG pool remains uncovered all winter as we have no trees around our home and it generally remains clear all winter long, as I close after the water temp goes below 60F. I checked the water temp today and it is in the mid-40's.

Any ideas as to why it greened up so quickly. Its only March!

[FormerBromineUser]

We had some hot, sunny weather for a while. Did you? Sorry about your pool....

[Slachey]

Yes, we did as I had stated in my post above. Although I would have been surprised if the water temp exceeded 60F, which I am told is the minimum temp that algae needs to grow.

[FormerBromineUser]

Yea, I was just thinking the sun might have warmed up the top layers. I don't know that algae CAN'T grow below 60, but I know growth is significantly slowed.

[Anonymous [GDPR] European in the UK]

Any ideas as to why it greened up so quickly. Its only March!

I had know idea algae had a calendar. Nutrient rich water and low chlorine is sure to allow algae to bloom albeit a little slower when it cooler. No cover and some nice sunshine and away you go.

I put my pool away in September with water temp at roughly 60F and won't open it again until June, done this several years and not had a problem but I have low nutrient water and a good dark cover, maybe you need to spend a little or keep the chlorine level up.

Over here we tend to say algae won't grow below 50F (10C) just to be sure I do add chlorine and run the filtration 24 hours before I remove the cover. Sunlight is one component algae needs to bloom.

[FormerBromineUser]

A clear explanation, Teapot. I agree that it must have been low chlorine and the sun. When you don't have a cover on the pool, I think you need to keep a close eye out as the weather warms.

[swimdaddy]

I had the same thing happen as spring came quite early here in the northwest. I just raised the chlorine with a gallon of bleach and all clear again, haven't even tested yet to know what my levels are.