I think right now what you have is just fine. Some people like the 2 goldfish per 30 gallon, I go by 10 gallon to every one goldfish. This doesnt mean you should stick one goldie in a 10 gallon, I would never go less than 30 gallons to have 2 or 3. Even then thats a tad bit small. You need to have a TON of filtration though, they are messy critters. You cant fit anything in there right now, your already kinda stocked. If you want to get a bigger tank, maybe go ahead with a loach.