Marine aquarium location may not seem like something you have to put much thought into but there are quite a few things to look at. The last thing you want to do is have to move it after everything is set up or even worse loose your fish. Find a location in the house where you will have plenty of room to work on the fish tank and do maintenance but most importantly where you are going to enjoy it . There is no point in having a aquarium full of beautiful marine fish or a reef aquarium in a room where nobody is going to see it. You are going to need access to electricity so choosing a location with a wall plug is a must. My old roommate had a aquarium that was hooked to a extension cord. They never determined exactly what happened but it ignited and the only reason the house is still standing was because the heat broke the aquarium and extinguished it . If the location that you want the tank does not have a outlet I would recommend having a licensed electrician hook one up for you. The room the tank is kept in should not be drafty (marine fish don’t like cold water conditions), avoid it being near a outside door or window that would cause a fluctuation in temperature. Depending on the size of the fish tank you need to determine if the floor is strong enough to hold it. You might need to consult with a contracter to determine this. Depending upon where you live you might have to get some kind of flood coverage in the event water leaks from your aquarium to the apartment below you. Carpet should also be avoided changing water is sure to lead to a little spill here and there that can not easily wiped up. Marine fish can be very nervous so having them in a high traffic area is not recommended. The aquarium should not be near windows or in direct sunlight especially if live rock is being used. Special aquarium lighting should be used to control the growth of the living organisms in the live rock. One last thing you need to look at is how you are going to drain and refill the marine fish tank with water. Having to run a hose through your house every time you do a water change could become cumbersome after a while. Having a water supply and a drainage point nearby should be something else to consider.