what does cycling mean
You can do a water change while it is cycling, but that might slow down the process.
An established aquarium is an aquarium that has gone through the nitrogen cycle. This is not "established" it is a "cycled" aquarium. The stage after cycling where the plants are reproducing and fish are growing successfully is an "established" aquarium. See related question on the nitrogen cycle.
aquarium means: alot of water surrondering the fish that live in it.
You mean substrate?
I have fish in an aquarium
That honestly varies from aquarium to aquarium. I would say maybe $10-$20 or so? Please be more specific WHICH aquarium you mean?
up cycling is not related to the sport of cycling. It is like recycling, but to re use the item to create something better/improve on it
An aquarium is considered an ecosystem because everything in it can live in the aquarium. Changes in the aquarium can mean life or death for the fish just as in the real world.
When I am cycling a tank, fresh or salt, I do not change the water. I maintain the water level (and the salinity), but I never change it. The goal is to let the bacteria build up and eat the bad stuff, so physically removing the bad stuff will only delay the cycling process.