I fell for the more is more pitch at the pool supply

I've been having filter problems for a while and neglecting other aspects of the pool. I recently noticed black specks on the pool floor and assumed it was a twig or broken up leaves. Now I have about 3 half dollar size spots and several small specs. I took a trip to the pool supply and bought black algae killer and filter cleaner. I was told that 36 hours after I treat the pool with the black algae killer, I must clean the filter elements because the elements are affected. I have a 35000 gal pool. I was told to then shock the pool with 4 pounds of "shock". Anyhow, I spent $165.

Souns like black algae, and unfortunately, once you have ie, it's really tough to get rid of. What type of finish does your pool have? Did you have any success with the treatment you used?

One of the larger spots is virtually gone. I just notice a mustard color spot in the deep-end. I am still scrubbing the smaller black spots with the metal brush but it does not seem to be making any difference. I treated the pool with the algae killer Friday. Can I treat it again? Should I clean the filters also? The pool is made from gunite and I'm not sure what the plaster/paste that they finished the pool with is. Thank you for your response.

Post a complete set of water testing results taken with a drops-based kit. Make sure that your CYA level is one of the things you report. What is the ingredient in the 'shock' you are using?