Granted the fish do get massive, the fish pictured above is quite a nice blue or fulton catfish. It is denoted by it's distinctively broader head from above, and it's flat margined anal fin, while the channel catfish has a rounded margined anal fin. Also the anal fin ray count is generally 35-36. This being said beware of the growth rates for channel catfish. I have two that have grown to more than 12" in less than 6 months. I got them at roughly 2". There is a member on here that has one at more than 3' in less than 3 years. I would say the best thing to do for your filter is to get some of the old cartridges from your friend's filter along with some of the water during their next water change. Cut the filter pads into small pieces and put those in your filter. make sure to keep them wet as not to kill the bacteria. use water from the filter to keep it wet. Second go to your local pet store and get some biological filter booster. These bottles contain millions if not billions of live bacteria that will help your filter start faster. Next I would recommend starting your next tank now without any fish in it. Go to your grocery or hardware store and get some regular ammonia. Put one teaspoon per 10 gallons daily to simulate fish urination and defication. This will do what we call a fishless cycle. It generally takes one to 2 months for the biofilter to setup. Until the ammonia and nitrates hit 0 ppm you should not put any fish in the tank. Do not test the water right after you put the ammonia in, but rather first thing in the morning before adding it. Going from a 10 gal to a 30 gal will do virtually nothing in terms of providing a home for you new pets. I would suggest your next tank be either a 90 or 125 gal, and then either a 250 or 500 gal. 500 gal might be suitable for life. Just remember that in the wild they get to more than 3-4' and I know several members with them over the3' mark. Hope this helps. PM me if you have any more questions.