I have a 30 thousand gallon pool. I have an in ground pool with a vinyl liner. My filter is old it has 3 cartridges in it. When I left an we had a little bit of black algae spots but when I returned almost the entire pool liner was black. I put 4 1/2 pounds of black algae in it and 6 pounds of super shock. I scrubbed it twice today and I have a few spots that are cleaned. I am breaking my back is there anything else I can do? How long does it take to get rid of this. Please help.