You have a lot of questions but you gave much more info than most newbies it makes up for it. LOL! I can't answer all your questions but there will be others along to correct that. No one pond is exactly like another and no ponder is just like another. I can't quite visualize your pond but maybe it will come clearer later on. You don't say why the pumps fail. If it is the same reason each time then I would think you should go to another type altogether. Or provide what it is lacking. If debris is damaging the pump then you need a prefilter which prevents damage to the impeller. Most pumps have a small and totally inadequate sponge in front of the impeller. Most of us toss it and install some sort of prefilter in it's place. Looking at your pump, I don't see even that, just a cap with lots of slots for water flow. Options could be change pump type, or remove filter cap and attach prefilter with sponge or other filter material. Algae is endemic when the pond gets lots of sun. You could use lots of chemicals but that is rarely satisfactory. A UV filter could work just fine by using a diverter or adding a small pump and filter. With your waterfall pump I suspect a separate pump would be easiest. More later, Sandy

Almost certainly, your canister filter at the base of the tank is blocked solid with sludge. This is one of the benefits of letting the oil tank run empty. Close the valve at the bottom of the tank and replace the filter. Clean the steel canister thoroughly, as well. Use gravity to purge the line to the burner. It may take awhile. When it looks pretty bubble-free, you should be good to go.

I just went through the same thing. Gunite and plaster pool, about 24000 gallons. Upgraded my old single speed 1-1/2hp Pentair Whisperflo pump with a Pentair VS pump. Replaced my Pentair Clean and Clear 240 cartridge filter with a Pentair Quad DE 100. The filter could easily be considered oversize for my pool, but the Quad DE will filter better than the old C&C, and the larger size will give me longer runs between cleanings. I like the "hybrid" aspect of the Quad DE. The ease of cartridges, the filtering of DE. I'm going to direct-plumb the filter, meaning no multi-port valve. I don't know much about Hayward, but I highly recommend the move to the variable speed pump. If they offer a 2-speed pump that might save you money on pump coast and running costs.

I called the company who installed the pool and they advised against this. Basically the pump should be near the pipe that feeds the water to the pump. So, I would have to have all the plumbing moved as well. Not a good solution for me at this time. I installed the filter system yesterday and so far so good. Probably saved $250 overall!