That looks like mustard algae, which can be a PAIN to get rid of. Green algae will typically die off with a good shock below 20ppm, but mustard algae can be resistant to a shock. So instead of throwing money at it in the form of chlorine and shock, check your local pool store for a "polyquat 60" product, or get it from Amazon. This stuff is specifically meant to kill mustard algae, and it works. I had a bloom last year I couldn't get rid of and made the mistake of wasting time and money shocking, and when that didn't work I found polyquats mentioned in my Taylor book (which I guess I should have read in the first place). Gave it a shot and within 2 days I think the mustard algae was gone.
Also, if you have the money, change your filter to a sand filter with a valve that allows for waste. It'll require less maintenance since all you need to do with a sand filter is backwash and rinse every now and then, and might even save you money in the long run depending on how often you need to change the filter cartridge.