welcome to the forum! and i guess the hobby!
I'll try answer some of your questions.
1. When you setup your tank you should let it cycle at least 2 weeks to get the beneficial bacteria (BB) established so that it will be able to handle the bio load (fish poo) that your fish will create. Cycling your tank also involves having a little knowledge in the amonia/nitrite/nitrate cycle which is really where 'cycling' orignated i guess. To simplify this fish poo converts into amonia, amonia in then evolves to nitrites, and finally nitrites into nitrates. Nitrates being the less harmful to your fish of the three. You might want to do more research into this so you gain a better understanding than my example.
2. You will need to add water ager / dechlorinator with the water when you are cycling. You should only need to add this once at the beginning when you have filled the tank, but also any other time you are adding water to your aquarium that comes from the tap. This removes any chlorine from the water which is harmful to any aquarium fish.
3.Water changes - I don't think it would be beneficial to remove all the water out of the tank at once because this would remove the beneficial bacteria (BB) that was established when you first cycled the tank. I believe that depending on the size of your tank you should at least do a 20% water change weekly minimum. This answer also varies with the fish that you are going to be keeping. As some fish poo more than others the more frequent and more amount of water you will need to change.
Is your 55g tank a standard 4ft? If not please provide dimensions..
They are not dumb questions, we all start from the begining at one stage, I think you would also learn a lot from the 'Search Forums' function on this forum, there are a lot of experienced fish keepers that have posted answers on other threads that you might find useful.
Good luck on your fish keeping!
