baseballfan111 said:
a very common begginer problem is they think that you can cycle with out fish.(you can but you have 2 buy a product and you cant have it with fish) what i think you should do is get some guppies, or danios and use them 2 cycle the tank, it will probley take 2-3-4 weeks, angels can not cycle a tank. When you are done cycling move the guppies or danios 2 a diff tank, they might nip at the angel fish. i would get 6 guppies or danios for the cycling. have fun!
You can certainly cycle without fish - in fact, it's recommended! And no, you don't have to buy a product. There are various ways of doing it, but ammonia, fish food and I've even seen urine used! You can speed it up by getting filter innards and gravel from an already established tank.
For a situation like this (i.e. upgrading an old tank), the easiest thing to do would probably do a direct transplant of the contents of the 20 gal into the 50 gal. I actually did this yesterday so I know it works!
What you do is use the old filter, old water and old gravel (being careful to transfer it quickly to preserve the bacteria). Put your fish in a bucket of tank water, spread the old gravel carefully over the top of the new gravel in the new tank, and set up your old filter in the new tank. You should run the old filter concurrently with the new (probably bigger) filter for a few weeks, to make sure the new filter is well matured with bacteria. Add matured water (you'll probably have 10 gal that isn't in the bucket with the fish), top it up with fresh water, allowing space for the bucketful, and finally add your fish. It usually takes no more than a week for the bacteria in the old stuff to colonise the rest of the gravel, new filter and water and if you're lucky, you won't even get a nitrite spike. Plus you'll have happy, happy fish.
What I actually did was even more amazingly cunning than that - I am using one of those cheap filters driven by an air-pump which I stuffed with the cut-up contents of the old internal filter from my previous tank. The only complication was that this pump had failed a few days before, so I was worried the bacteria had died off. However, there had been a flow of oxygenated water through it, from a matured sponge filter I had running in there, so I thought it would be better than entirely new innards. You know, that cheap filter is working great. Is it possible that these elaborate and expensive filters are all a con?
I ought to add that all my tanks have plants in them, which can act like a natural filter.