Red cap oranda and black moor Qs?

I am glad that there is somebody rsponsible enough to give their first goldfish a good sized home. Goldfish can grow at different rates, depending on water quality and diet. You do have a varied diet for them, but they should be fed less, about 2 or 3 crisps a day, each, plus a few mini sticks. They use up much less energy than we do, and therefore need much less food to sustain themselves. It could take as little as 6 months for them to reach the size at which they need to be transfered to the 55 gallon, but size is a much better way to measure this. At about 4-5 inches they could be transfered to a larger tank. Your water changing procedure is great, and the better the water quality, the faster they will grow. Just remember, don't overfeed them - they won't grow any quicker, and they'll just get fat. good luck :D