Kherb

Hello, I’m pretty new to Pool stuff but was doing well until 1 or 2 weeks ago. Then algae arrived and I began researching. The first time I just shocked the pool. Talked to a pool place and they directed me to brush the pool and then shock (makes sense). So I brushed the pool and shocked it again. I made sure the filter cartridge was rinsed and had the pump running. It went away for a day or two. The cover doesn’t stay on completely and it stormed. Algae returned. So I brushed the pool and shocked again. Filter rinsed several times and pump ran. The next day it looked better so I tested the levels and added what I needed. It’s back again. The pool isn’t at my house and my girlfriend isn’t always able to keep up with it. So I’m thinking of just draining the entire pool (good opportunity to also remove an annoying rock under the floor). Is this a good idea just to start over? Once it’s filled I assume I test the water and add whatever is needed? Do I need to shock it right away? My pool is a Polygroup Summerwaves 12’x30” RX 600 series. It holds 1,471 gallons (5,568 litreS) I’m going out to buy cartridge cleaner to ensure all algae is killed from the current cartridge filter. All stores and pool centres are completely sold out. Amazon’s won’t arrive until September so I need to ensure the one I have lasts the rest of summer. Any help, suggestions or tips are appreciated. Thank you in advance!