Hi Marlene, The 4 on your test kit is PPM. Match up the colours look at the corresponding number and that is your PPM. To clear up your algae your going to have to maintain a chlorine level much higher than 4PPM. Get a bottle of distilled water and make a mix of 3 parts distilled water and 1 part pool water. Fill your test kit and take a reading and multiply the results by 4, that will be your PPM. You are going to need to be in the 15-20PPM range to knock down your algae. Get your chlorine up to that level and keep it there as consistently as possible by testing frequently and adding bleach as necessary.