Hello and welcome to TFP! We can help if you are willing to do a couple things:
1 - You must have the proper test kit. (see TF-100 link below) The proper test kit is everything. Why? Because we've all learned (from personal experience) you cannot reply on pool store tests, test strips, or simple over-the-counter kits. They don't read Free Chlorine (FC) or Cyanuric Acid (CYA) levels accurately or to the high levels we need.
2 - Avoid the pool store for testing, advice, or products. You simply won’t get the advice/service you deserve and you will waste money on products your pool doesn’t need. Do not add anything to your pool other than what is advocated by the TFP site or its experts.
Algae means you need to "SLAM" your pool. Not shock or spike, but SLAM.
SLAM is the term used when we “Shock” our pool to a higher “Level” of Free Chlorine (FC) and “Maintain” it that way until 3 objectives are met:
1. Water is clear
2. You do not lose any more than 1ppm of FC overnight (that's the OCLT)
3. CC (Combined Chlorine) is <.5
** You MUST meet ALL 3 items above to properly do a SLAM. Simply “spiking" the FC higher than normal isn't SLAMming, therefore there’s a good chance your algae will return.
If you are ready to take charge of your pool and have sparkling clear water, just follow these procedures and you'll be on your way. But #1 priority is that test kit.