If you have a light green pool you need to shock your pool in order to kill algae (add more Acid and Chlorine than usual).
Algae feeds off high pH and your chlorine isn't as effective when your pH is high, you need to lower your pH using hydrochloric acid. 1-2L of it to start with. Be careful when adding it to make sure it doesn't splash up on you as it is highly toxic and dangerous, and only add 1L every 24 hours if your pool is Vinyl lined as it's more sensitive to harsh chemicals.
You also need to shock your pool with chlorine, 2 cups/400 grams of granulated chlorine (not stabilized) or 3 tubs of 15L chlorine (as it's actually only 20% chlorine and the rest is water), or if your pool is salt water chlorinated adding 2-4 bags of salt (once again you should get your salt tested at your local pool shop to see exactly where it's sitting) and turning your chlorinator to 100% for a couple of days to really boost that chlorine and get that water sanitized. Your salt should be sitting at around 5000ppm (parts per million) and each 20kg bag of salt equates to 500ppm.
If you've added your salt and turned your chlorinator up to 100% but after a few days theres still no or next to no chlorine being produced or your "low salt" light is still on even though you know there's plenty of salt in there, your electrode may need replacing. An average life span for an electrode is 3-5 years. You also will need to clean your cartridge filter or back wash your sand filter, and ensure all of your skimmer baskets and pump baskets are empty.
If the green in your water has set up home on your pool steps and doesn't want to move out (sounds like my mid-twenties children) adding hydrochloric acid should slowly start killing the algae on your steps as well, if your pool is concrete you can use a metal brush or if your pool is vinyl you can use a normal plastic bristle brush to help brush this algae off.
Mr Pool Man can't sell or ship Hydrochloric Acid, Liquid Chlorine, Granulated Chlorine or Salt online as it's either dangerous materials or too heavy, though you can grab them from your local pool shop.
We recommend testing your water a few days after this heavy dose to check your levels. You can do this yourself using a 7 in 1 Test Strip Kit.
Once your pool is sparkling, don't forget to add 500g-1Kg of Stabilizer/Cyanuric Acid/UV Blockout to keep that chlorine in the pool and not being sucked up by the sun. Adding 500g of Stabilizer once a month should keep this in check.