If your biggest problem is water quality, start by improving or adding filtration. But to me, that looks fairly clear, for that large of a pond. Next, to protect your fish, you either have to net it, or set up protection at least in the area you feed the fish, along with adding more places that are safe for fish to hide. The tires leach chemicals into the water, and will continue to do so for a very long time. Plain unglazed terra-cotta pots, pvc pipes, and new never used heavy duty plastic bins such as the pans used for oil changes or the heavy duty kitty litter bins are good substitutes. The clay pots if set on their sides, provide places for smaller fish to hide. They can also be used for growing plants. On the pvc pipe, you can get some very large diameter pipe and set them for the larger fish to hide. These are to provide shelter from herons. If the pipe edges are roughy from cutting, you’ll want to do a quick sanding to smooth sharp edges.
The kitty litter and oil pans are ideal for growing plants, which will make the fish feel safer, provide food, and places for the fry to hide.