If it's filtered, it won't really make much of a difference on the water changes unless it is a seeded filter, otherwise I wouldn't really bother since you'll still have to do at least somewhere between 25-50% water changes at least every other day, twice a week is minimum for a healing fish. Once he starts to heal up you can ease off the water changes and just make sure the water is still healthy and he's getting good food.
Are the bloodworms freeze dried? If so, can you get frozen instead? The more blood in bloodworms, the healthier they are so it would benefit him. Any frozen foods are great so daphnia, brine shrimp, mysis shrimp is definitely good for him as well. You can feed those to your other fish as well as they are just really great.
As for pellets, I want to recommend New Life Spectrum for you. Hikari is okay but they've gone downhill in their ingredients in the past few years, they used to be good. However I only trust their frozen foods, I don't like the San Francisco Bay ones or any others honestly. But the cheap foods use fillers in the food, same as cat and dog food as well. You want to stay away from fillers as much you can for a good quality diet, these include Wheat, Corn and Soybean. It's just hard for the fish to digest those, however Wheat is alright since it is only used as a binder but you don't want to see it as the first ingredient. The first three-four ingredients are the most important (though animal foods are not required by law to list ingredients in order of weight like they do people foods) and you want to see whole fish meals or krill or spirulina.
NLS also contains garlic which I'm a huge fan of, it's a natural anti-parasitic food so it will help ward off internal parasites and it's very tasty to our fish so they'll love it as well.
