Controlling algae in stock tank

We finally have got our stock tank going.  It turned out being a two year project; tapped into the drain line that drains our alfalfa field two years ago, last year we set the tire tank, and this year we finally got the submersible pump and solar panels in.  We have a two one hundred watt solar panels, and two one hundred amp hour battery backup.  The intent is to have it pump 24/7 to keep the tank from freezing up in the winter.  As this is the first time dealing with solar it has been a learning process.  It is looking like we are going to have to add some solar panel; at this point we can't produce enough power to keep the pump running and recharge the batteries, so may add two more panels, and we have been thinking of adding in a 400 watt wind turbine.  

 

So now that we have the tank in place we have algae growing in the tank and I would like to be able to control it.  I hate to add in chemical because with the tank constantly changing water it would just get washed out.  Does anyone have any ideas.  If I put a couple of gold fish in the tank, do you think they would survive the winter.  

 

Battery  bank is in the box behind the solar panels, I used an 1 3/4 solid core door with 2" of foam insulation.  I sized it so that I could get three batteries in the box.  I think that should keep them from freezing.

We ended up having to change the discharge of the water above the tank, as when the pump shuts off with the water

 

We tied into the drain line on November 17 two years ago.  Needless to say it was not real warm to be in that water.  We started trying to keep the water out of our boots, but ended up in water up our waist.  I was never so glad to get out of that water.  We had a pump but it did not work all that well.  I am glad to see it in, and the cows seem to like the clean water.  

 

Controlling algae in stock tank