Aquariums can make an enormous impact on the atmosphere of the room they're placed in. Depending on why you are wanting to keep an aquarium in the first place, you may already know exactly where you want to put it. Or you may still be trying to figure that out. For the most part there are few places that won't work for your aquarium. You can put it wherever you are most likely to see and enjoy it.
But there are some considerations that will help you avoid problems.
This is not an absolute must, but often not placing your aquarium directly next to a window will help avoid some algae problems. Depending on your setup and the layout of your home, though, you may not have any problems if that is where you choose to place your aquarium.
Algae growth, like plant growth, is directly related to the balance of light, nutrients, and carbon dioxide. When these factors are perfectly balanced, plants thrive. If that balance is skewed, particularly by an overabundance of light and/or nutrients, algae is very likely to grow rampantly.
Direct sunlight supplies an enormous amount of light. Far more than the vast majority of aquarium lights. Unless you are meticulously planning for that amount of light, it is almost guaranteed that an aquarium sitting next to a window that gets a lot of direct sunlight is going to have a lot of algae problems.
However, if your window doesn't get as much direct sunlight then you may not have these problems. Perhaps you have a lot of trees that keep your window mostly shaded. Or maybe you live in a big city high-rise where the building next to yours blocks out a lot of direct light. If your window supplies a more moderate amount of indirect light you may not have any algae problems.
Whatever type of setup you choose to create, there are going to be periods of time that require a fair bit of work and effort. If you have a poorly planned location for your aquarium, this could potentially lead to a huge amount of frustration fairly quickly.
Think about how you are going to perform routine maintenance such as regular water changes. Are you planning on filling up your tank using water from the tap in your house? If so, is there a tap close to where you're going to put your aquarium, or are you going to have to run a hose a hundred feet? Are you going to have to buy water? If so, is your tank going to be fairly close to your entrance or will you have to carry it through the house?
When you drain your aquarium, how are you going to dispose of the water? Is there a drain close enough you can run a siphon to or will you have to drain into a bucket and then carry the water out? Imagine performing a 50% water change on a 225 gallon aquarium you're keeping in the basement if you don't have a drain down there and have to carry the water up the stairs in 5 gallon buckets.
Also think about moving your aquarium in and then (eventually) back out again. Is it worth the extra effort to have to squeeze and finagle it through tight turns and doorways to get it into a specific room? Ideally, you'll pick a room with easy access that allows you to fill up and drain the aquarium with a minimum of manual work.
Do You Need to Worry About Your Floor?
Water weighs about 8.5 pounds per gallon. Add in the weight of the glass, substrate, and any additional rocks or decorations and you can estimate your total weight to be around ten pounds per gallon. The most popular size aquarium has long been the standard 55 gallon aquarium, which is going to weigh around 550 pounds.
Some people get extremely concerned with the weight of their aquarium and whether or not the floor in their house will support it. Is this a concern that you should be thinking about before bringing your aquarium home? Most of the time, no. Unless you're going larger than about 125 gallons then odds are you won't need to even think about it.
There are a huge number of factors that determine whether or not your floor will be able to physically hold the aquarium.
What is below the floor itself? If your flooring sits directly on the concrete foundation, as is often the case in basements and garages, you can probably put just about anything you want on it without having to worry.
Most houses are built with joists, which are long wooden beams that are spaced out with the floorboards resting on top of them. The joists themselves are usually extremely sturdy, though the age of the house may impact how strong they are. The older the house, the higher the chance that some sort of damage has weakened the joists. Conversely, though, older houses are also more likely to have thicker, harder beams that may give more support.
How much your tank weighs and how it's distributed on these joists will determine how well the floor will hold it. If the tank is sitting perpendicular to the joists, the weight will be spread out between a number of different joists, making the tank more secure. You may run into trouble, though, if your tank is sitting parallel between two joists with only the floorboards supporting it. The closer your tank is to where the joist is connected (generally at a load bearing wall) the more secure it will be. Exceptionally heavy tanks that are situated near the middle of the joists may, over time, cause the joist to bow or eventually even break.
For the most part, though, the typical tank will never have to worry about this. It would be rare that a 75 gallon aquarium would run into problems, and even 125 gallon tanks are typically fine. But if you are willing to make the investment for an aquarium large enough to hold several hundred gallons of water, it would probably not be a bad idea to hire a structural engineer to inspect your floor to determine if you need to add additional support.
Keep It Level
It's not uncommon to come across debates about how much of an impact not being level can have on a fish tank. Some people will argue that a tank not being level puts it at an increased chance of cracking or breaking its seam (leading to all of the water in your tank gushing out onto your floor). Others will argue that even relatively unlevel tanks don't create any forces that are outside of the accepted tolerances for the materials (the glass and silicone) the tank is built with.
Wherever you stand on this debate, it doesn't hurt to be safe. When setting up your tank, find a place that is flat and level. If you set your tank stand somewhere and it wobbles, either move the stand somewhere else or add some sort of support such as composite plastic shims to stabilize it.
There are no places that are necessarily "wrong" for your aquarium, but anticipating and avoiding potential frustrations and problems can increase your overall enjoyment of your aquarium.