Can I put a catappa leaf in a goldfish tank? Is it necesary to put live plants in a pot?
If so, where can I get a pot for the plant?

I have never heard of catappa leafs... Looking up about them, it seems to be an Indian Almond Leaf?

Found an article here about it, although it mentions nothing about goldfish- (Link is not visible to guests. Please register to view.)

I really don't know if they're goldfish friendly I'll post in another forum I belong to, tomorrow about it, I'm sure someone there might know  

As for live plants, a pot with some aquatic soil and large rocks on the top would be fine, or if you have suitable substrate that the plants can grow their roots in that would also be fine What plants were you considering? As goldfish will eat most things

Okay so on those catappa leaves, see the thread and responses here; (Link is not visible to guests. Please register to view.)

Generally all the leaves will do is soften the PH, goldfish don't really need a soft PH and so catappa leaves are in no means necessary but won't harm the goldfish -although as people mentioned on the thread do keep an eye on your PH if you do decide to use them.

As for live plants, be careful of what types you get, goldfish are omnivores and will eat plants