Help me with dead algae dust please!!!

Hello...

I have been dealing with an algae issue which I never was algae until recently. I have this sandy/dust looking stuff in the crevices at the bottom of my pool that never seems to go away with vacuuming. At first I thought it was dust/dirt from cutting the lawn and things blowing around in the yard getting into my pool but then realized after getting a brand new liner put in and dealing with the same prob a week later with all new water and not cutting the grass that it is something else. I have a cartridge filter and did not get a new cartridge with the new liner. Long story short I used flock, and clarifier and made more of a mess in my pool. Fast forward to now and I am getting the water clear again but dealing with this dusty debris accumulating at the bottom again. I use a skimmer sock because my cartridge isn't very good at catching the fine particles. The sock is so gunked up after I vacuum with this fiber type stuff that looks like chunks of wet paper bag or brown insulation type stuff in the sock. I am constantly cleaning the sock out and leave the pump running 24 hours a day. Last night I super shocked it with 3 jugs of liquid shock. My pool is a 24' above ground 13,500 gals of water. Am I supposed to do something to clean the cartridge other than just hosing it off? Do I need to add an algaecide? I am ready to tear the pool down because this constant battle of hand vacuuming this stuff is making me so crazy! I do not have an automatic pool cleaner its all me. Would buying a robot cleaner for the pool help? How can I finally be rid of this stuff without emptying the whole pool? Thanks