According to the farmer at https://www.hanoverkoifarms.com/ , it is also important to "maintain the proper kH/alkalinity", give the page a read if you are in the mood for a good rant.I didn’t think blood worms were good for goldfish.
As for water tests, 0 - ammonia, 0 - nitrite, and 10 - nitrates, I do weekly water changes in the tank and keep the nitrates below 40ppm. They are at 40ppm when I do my water change at the end of the week (water change is approximately 80-85%).