I'm not much of an expert, more like a knowledgable amateur when it comes to aquariums. We currently have a 55 gallon tank (thanks Diane!!) and a 20 gallon tank set up. We have the worlds most expensive feeder fish in the 20 gallon tank. 3 x $0.25 for the fish, being maintained by well over $150 of aquarium stuff. The 55 gallon is filling up with Platy's who are breeding like rabbits. We have 5 adults and about 15-20 babies now. None of the fish have died so I must be doing something right
The first questions to answer are; what size tank are you thinking about buying and do you want to do fresh or salt water fish? Oh and after that probably the next question is how much are you willing to spend? Aquariums are like race cars, as in there is an aquarium for just about every budget level.
As far as which store to go to I'd steer clear of Walmart type places. Mega pet stores like Petsmart are usually ok and the people working there have some knowledge but it's hit or miss. For the best advice you have to go to specialist stores. For example here is how our recent inquiries into how to put live plants in an aquarium went.
Walmart: Plants? the garden section is over there.
Petsmart: Plants? We have some here, I think all you need is smaller gravel and they be fine.
Fish world (on Capitol Blvd in Raleigh): Plants? sure we have lots of plants and here is the best gravel to use with them, oh and they grow much better if you use this type of light bulb. We have this 2 page handout with everything you ever wanted to know about keeping live aquarium plants healthy.
Other advice:
1) If it is for an office, they do have services that install and maintain aquariums, if you go that way the cost would probably even be tax deductable as a business expense. It's good to screw the IRS
2) Get the best filter you can afford and also think about how easy it is to service. The 55 gallon tank we got from Diane has a Magnum 350 floor unit (did I mention Thanks Diane!!). It works extremely well, but it is kinda a pain to change the filters out.
3) Don't use city water if you can avoid it. I think even after using the chemicals they have to neutrallize the chemicals in it, it isn't as safe for fishes as natural water out of a well. Good fish stores sell RO (reverse osmosis) water as well but that might be a bit of over kill, but it is probably the best of all options.
4) Be realistic about how much time will be spent in maintaining the tank. Goldfish don't care so much if the water quality or temp varies over a wide range, delicate tropical fish will probably start to croak if you miss a filter change or tank cleaning by too many days.
If you have any other questions let me know.
Shawn