An aquarium is what you call a place of life or a vivarium that is used for maintaining life-forms of a marine nature. In almost all cases, the aquarium has at least one side that's made of see-through material, in order to allow people to see or observe the creatures living inside of it. If you are someone who maintains an aquarium, then you would be called an aquarist! To be an aquarist, you will need to dedicate some part of your daily routine to the process of maintaining the aquarium, something that goes without saying.
However, before you can go about buying an aquarium and buying living creatures to stay in it, you need to consider many things that will help you understand the intricacies of maintaining something like this. There are special features and conditions that pertain to different kind of living creatures and based on what kind of effort your are willing to put into this hobby, you can pick one from many.
The Casual Hobbyist
The most basic kind of aquarium that you can install in your home or place of work is a bowl. Ideal for keeping gold fish, the bowl is an example of how simple these creatures can be, even outside of their natural environment. While placing these fish in a bowl may seem like restricting their space, the thing about gold fish is that they have a memory span of 2 to 3 seconds, which means that the bowl seems like a new place to them every few seconds.
This kind of an aquarium requires the least effort from your end. All you need to do is feed the fish based on three basic rules of fish-keeping - Feed them the right quantity of food, do not overcrowd the aquarium and partially change the water every single day. That's all you need to do and your fish will live a happy and long life in that tiny little bowl. You get bowls of various sizes if you feel like keeping something more than just one lonely fish in there - that should liven things up inside.
Alternately, you can even get yourself a small turtle-tank, where you have one or two of those tiny turtles, a bit of water and a bit of sand & rocks. Once again, don't overcrowd them and don't over-feed them, while the water can be refreshed every few days. That's good enough to ensure that they remain healthy and happy in their new living spaces.
The Fish Lover
Now, if you are willing to put in a bit more time, then you might want to consider an aquarium where there's a lot more happening. That means, more fish or fishes, a nice base of gravel and sand as well as a relatively more complex filtration and temperature maintenance system. With all this going into the tank, the size of the tank also has to increase and the basic requirements to maintain all these elements will also require a bit more work from you. If you enjoy these water-creatures and their habits, then you won't mind putting in the little bit extra into it.
Alternately, if you have a lot more time and patience, you could even go for a bigger tank or a salt-water aquarium that allows you to keep even more exotic creatures and fish(es). The salt-water aquarium is like the ocean or the sea and the kind of beautiful creatures you get to keep in there are just incredible! They are much more diverse and interesting as compared to the fresh water creatures but maintaining them requires a lot of time, effort and, most importantly, knowledge. You cannot and should not start with a salt-water aquarium but if you're quite good with your regular aquarium, you might consider getting the added instruments required to maintain this kind of a viewing tank.
Some Basic Tips
The first thing that you will need to consider is the cleanliness aspect of the tank. This is the part that requires the most attention and begins from the feeding process. The amount of food you give to the fish(es) will depend on the number of fish(es) you have. You need to give them only that amount of food that they can finish off in one sitting, so to speak. This might take a little bit of time and you might need to observe their eating habits every single day, but depending on the kind of food you are giving them as well as the kind of eating habits they have, you will need to ensure that there's no waste food in the tank any more. If you do find uneaten food floating around or inside the tank, get it out!
The next step is to maintain clean and healthy water inside the tank. Even though you might have a filter in there, you still need to change about 20% of the water in the tank, every single day. That helps the filter do its job by easing some pressure on it and also gives your fish(es) a cleaner place to stay in. Now, don't go ahead and change a whole lot of the water, or even all of it, at one go - that might do more damage than good. Think of it like a home for the fish - they spend their time getting familiar to the place (the water they are in i.e.) and they grow fond of the quality of water and its contents.
Then, if you just change the entire water, it's the same as taking you out of your home & city and putting you in a new place every single time. You would take time to adjust and by the time you do, you are being moved again. That is just too nerve-wracking for a fish and you should allow them to settle down before anything else. Once a month, you do need to carry out a thorough cleaning and that means, taking the fish(es) out into another container and draining the entire tank of all but a tiny bit of its water. Clean out all the filters and thermometers and rinse out the sand and gravel, using a sieve, and put it back together again.
Never use a commercial cleaning agent or a detergent to clean your fish tank or the equipment that goes into it - that could be fatal to its inhabitants, as could be overcrowding of the tank. Fish need their exercise and if you fill up the tank with too many creatures, they just might not have enough space for themselves. So make sure you give every creature what it needs and have a happy and smiling aquarium at all times.