I'll probably do 6 of them. I'm planning on getting a fx4 filter will that be too much for the goldfish?Could probably swing 5 or 6 of them. Maybe even up to 7 depending how much work you wanna do. Just keep in mind goldies are dirty fish. The high end of stocking means changing a lot of water. A good basic rule of thumb for fancies is 20-30 gallons for the first, and add 10 gallon for each additional.