30liters is approx 8 gallons. Which, I believe, is too small for 1 black moor. I'd rehome the goldie and find more suitable fish. You could heavily plant the tank and have a school of 6 neons. In your tank, you're a bit limited on what you can get. A single male betta would love the tank, could maybe even squeeze 2 or 3 amano shrimps with him. BioOrb....sounds circular right? I don't think you could divide it well....was thinking(if you could) divide it and get 2 male bettas. But I don't think you will be able to divide a circular tank.
If you're wanting to stick with the goldie, here are some facts you should consider. They poo....ALOT. They produce alot more waste than some fish and thus create more ammonia, which means they need higher grade filtration. Double than what your tank would come with. With a tank that small, you won't be able to add more fish. The bio-load would be too large for the tank to handle well. Your black moor maybe small now, but his genetics say he will grow atleast 10". Which means you will have to upgrade later on, likely within the year you have him.
Last edited by FishyFishy89; 05-02-2013 at 04:05 PM.