I looked over all the posts in this thread.....seems to me you started trying to shock your pool on the 9th, but didn't really get going till the 15th. Which would mean you haven't been shocking your pool for a full week yet (even though it might feel like forever and i read where you started thinking about getting it cleaned up over a month ago).
Another thing i noticed was how much you have learned so far, congrats you are getting there and once you get it all down you'll be very happy!
You mentioned buying filters....i'm curious as to why? I can understand having two, so that you can just swap them out when one needs to be cleaned. How are you cleaning them? You can squirt them off with a hose, but if you find they aren't getting as clean as when they were new you should soak them, perhaps overnight.
Have you read this yet?
re-how-to-clean-a-cartridge-filter-t4465.html
Go read it all, but here is the basic info
What is the procedure to clean my cartridge?
Remove the cartridge from the filter housing following the manufacturer's instructions.
Use a garden hose with a straight flow nozzle to wash down the filter element. Work from the top down, holding the nozzle at a 45 degree angle, and wash all the pleats with emphasis between pleats.
Rinse until all dirt and debris are gone.
For all spa cartridges and elements used in swimming pools where perspiration, suntan lotions, and other oils are present, soak the element for at least on hour (overnight is most effective) in (1) a commercial filter cleaner; or (2) one cup trisodium phosphate (TSP) to five gallons water; or (3) one cup dishwasher detergent to five gallons of water.
Rinse the cartridge again to remove oils and cleaning solution.
If the filter has a coating of alage, calcium carbonate (residue from calcium hypochlorite), iron, or other minerals, soak the cartridge in a solution of one part muriatic acid to twenty parts water until all bubbling stops. WARNING: Failure to remove all oils and cleaning solution before acid soaking will result in a permanent restriction of water flow and cause premature cartridge failure.
Rinse the cartridge clean and reassemble housing.