For many years, I've known that Goldfish need 5 gallons each, until I was brought to MFT, I learned several new things. It was shocking to see that Goldfish need more room, so I've gone with the 20/1st-10/2nd+ rule and I share that info with the customers. Also, I've known for Goldfish to be slow growers, but now people on here are saying Goldfish grows fast.
Many information changes with time and we all learn new things.
Technically, Diane, the 10G is too small for 2 Goldfish. If I'm not mistaken, there is a Goldfish that is very small (dwarf), but I dont remember the name of it. They only reach an inch or two?
There must be more air supply in a Goldfish tank. I have 2 of 18" airstones with one air pump suitable for 30-60 gallons with two lines. Goldfish produces excessive waste and good water circulation is a must. Think of it, do you like going outside for fresh air? The same for Goldfish, needing fresh oxygen in the water.
Plus, more oxygen will be beneifical for the bacterias in the filter.
Thunder