Some pools are just more likely to have algae than others. The following are a few things to check for if you are constantly battling algae.
1. Circulation – Check your filter to make sure it is clean. Check to make sure your return lines are sending the water in a clockwise direction around the pool (they should not make the water ripple).
2. Chlorine Level – This should be at 3 parts per million. If it is low add some more chlorine. Also get a floater and keep it full of tri-chlor tabs. If you have a salt pool you can turn up the production to 80% to 100%. Remember salt cells don’t work well in cold water so you may need to check your salt level which should be at 3000 to 3400 ppm.
3. PH Level – This should be at 7.2-7.8. (Salt pools always have a high PH around 7.8-8.2) If the PH is high add a little acid.
4. Phosphates – This is often missed. Your phosphate level needs to be less than 200 ppm. A lot of people don’t know what phosphates are or how they can get into a pool. Fires, leaves, dirt & sun tan oil all give off phosphates. It is just like fertilizer & algae loves it. If your phosphates level is above 200ppm algae will grow even when you have a very high chlorine reading. To remove them you need to get a phosphate remover. There is a product out there called phosfree that seems to work very well. However if you have a cartridge filter you will have to replace the cartridges after you treat the pool.
Good luck and ask your pool man for help if you are having alge problems!