Originally Posted by em1981ma
3ft3inchesx1ft and a halfx1ft and a half
Biggest possible tank for the Goldies.
Also you can buy and add the new filter to the tank you are running right now to get the media in it to cycle.
Also since I am not sure if you use filter pads or ceramic rings or stars or something for media, I will comment about this... if you can fit the new filter onto your current tank, you can run them together while your BB builds.
If it will not fit the tank WITH the other one there are a couple more options for a smooth transition for the new tank. You could buy some of the pads or media needed for the new filter and add it to your existing one, if that won't fit you can always get a good start by taking a bag which is used for holding filter media and activated carbon, fill it with the loose media, hang it in the tank next to the intake or outflow. If it is filter pad(s) just add 1 or 2 in the tank in the same area so BB can start growing on it.
Here is the link for the Coldwater fish here on the forum
Freshwater & Brackish - Coldwater, Native Fish & Ponds - Aquarium Advice - Aquarium Forum Community
And this is the sticky from there, but you MUST see this and it will help to clear things up about the fish and tank sizes!!!
Why fancy goldfish require big tanks- visual perspective
I think the minimum is 20G for the 1st fish and 10G for each additional Goldy.
The best possible thing for their temp requirements is to separate them. Next best for the time being would be to get as close as you can to the temp needed on the low side for the temperate fish and the highest possible cool water temp. The warmer temp for Goldies raises their metabolism and thus can shorten their lifespan is what I understand as well as make them susceptible to disease/illness.
I kept a couple young ones in my Tropical community tank for awhile when they were tiny and I didn't know any better, then I temp adjusted them until I could get a new tank just for them. They can out fine. But not best for a long term solution.