Pool owners tend to overreact when their pool starts to go green.
There are only two reasons why your pool will go green.

1. Lack of, or poor circulation
2. Lack of chlorine

There are a wealth of reasons why your pool may not be circulating properly and one needs to familiarize ones-self with how your equipment should operate.
The pump draws water from the pool via your skimmer, and forces the water through the filter.
Once this has been done, the water is returned to the pool usually through one or more jets.
In the warmer months, pumps need to run at least 8 hours per day to maintain good circulation If your skimmer baskets were clogged with debris, this would restrict the pump in circulating the water.
Your pump basket is another place that could accumulate debris causing this restriction too.
If your filter media hasn't been changed for a while or needs backwashing, this would also cause a restriction in water flow.
Leaks in your suction or return lines are the most common form of poor circulation so if you are suffering from any of these, it may be a good starting point to familiarize yourself with how your pool operates.
Algae thrives on warmer weather and if you don't maintain a good level of chlorine in your pool it will surely go green in no time.
If your pool is too far out of balance, your chlorine wont be as effective in doing its job.
There are other chemicals that can assist the chlorine in keeping algae under control but this can be very expensive if it gets out of hand.