Algae under my Winter Cover?


I live in NW Indiana and have an in-ground pool. With all of the rain that we have had, the pool water needed to be pumped down.  I took off a corner of the cover to put the pump in and there is green algae everywhere.  Is there a chemical I can put in the pool to kill the algae off now, with the pool being closed?  In my 30 years of owning a pool, this is the first time I have ever had algae.

The chemicals were perfect when I closed the pool at the end of September.  I did have a big problem with our fill water this year, along with everyone else that has a pool in NW Indiana.  Three towns had been adding a lot of copper to the water, so our pool water was always out of balance with chemicals and cloudy.  Could this be the cause of the algae?

Vinyl Liner Pool Opening Series Green Water (4)
This is Algae
Hybrid Pool {HOF} Green Water
This is high metals (iron) in the water causing discoloration.



With the copper issues you had I wonder if you have a film of copper on the pool surface, or if indeed algae is growing. They could look similar (green and powdery).

If it is algae and you have a gunite/fiberglass pool you can add liquid chlorine (1-4 gallons depending on the size of the pool) to keep it under control. You can also use liquid chlorine on a liner pool, (do not use powder as it can bleach a liner). You’ll want to adjust the amount, again 1-4 gallons to the pool. If you add liquid chlorine and the green gets worse, I’ll look more to copper as the culprit. Higher levels of pH introduced by the chlorine could push metals out of solution, causing the water to discolor and/or deposit on the pool surfaces.

You can also add a winter algaecide (available online or though local pool supply stores) to keep it under control.

If you think it might be copper, I’d add a sequestering agent to the pool, a stain and scale preventative and then plan on using filtration to clean in the spring. If it stains the pool you’d be able to acid wash a gunite, or possibly chemically treat in the spring. If it stays too long, a liner may have to be replaced.

Hope this helps, please send more specifics (type of pool) and even a picture of what it looks like for more help. A pool store could also run a copper test to see what the copper concentration in the water may be.