If you have a heater crank it up (slowly as a big heat spike will kill fancy goldfish lickety split) to 82 and it will disappear much faster and won't recur at that level. Whenever you change water it stirs up substrate and it removes much of the bacteria that neutralizes ammonia. Try to not feed them for a day after changing water. Also don't feed them too much twice a week is plenty for gf. If you feed every day meals need to be very small. You don't need tons of filtration (or necessarily any) or tons of water changes but you have to be consistent. If you do a big change a couple times a week then don't change it for a month and overfeed them a bit that's a recipe for killing off your fish.
