Hi there!
Sorry to hear you are having problems with your tank. Starting out is a rough time for many new fishkeepers.
When you say you let the tank stand for two weeks, what did you do during this time? Did you add ammonia/fishfood to start building a bacterial colony in the filter? Or did you let the tank run without adding anything?
Unfortunately, fishkeeping is rather more complicated than short beginners books and fish stores let on. In many cases newbies are advised to let the tank run for a few days/weeks and then simply add their stock at 1 or 2 week intervals. This puts the fishkeeper into a
fish-in cycle without really telling them what it is. This wisdom is passed on from shop or book to fishkeepers who then pass it on so it is very possible to get this advice from friends and relatives as well.
What actually happens in a new tank is rather scary. When added, the fish produce waste. This is then broken down into
ammonia, which is then broken down into
nitrites and then
nitrates by very special bacteria in the filter. However, it can take up to two months for these special bacteria to grow into big enough populations to keep the water clean. In the meantime, the ammonia and nitrites are very dangerous to the fish and lead to what is often called
new tank syndrome. Symptoms of this are sick fish, fish constantly at the surface or even fish dropping dead out of the blue. Unless the new fishkeeper tests their water with a decent (ideally liquid) testing kit, the new fishkeeper has no idea what is happening and it can be pretty scary!
In order to handle this fish-in cycle safely, the new fishkeeper needs to test their water daily (and even twice a day if the water is bad) and change as much water as necessary to keep ammonia and nitrites at ZERO. If the fish are over-exposed to ammonia and nitrites, they will get burns on their fins and gills, become lethargic, be unable to get enough oxygen from that water and eventually die. Sometimes they will seem fine for weeks or even months and suddenly get really sick as their bodies give up due to the exposure to these chemicals. Nasty stuff!
So what you need to do now is get your water tested and buy yourself a decent master test kit that has ammonia, nitrites, nitrates and pH tests. A good one is the API Freshwater Master Test Kit. Avoid the strips - they are not as easy as they look and often give false readings. Plus they are more expensive.
Once you've tested the water, post the results here and we can help further.
Have a read of the stuff here about setting up a new tank and cycling -
Linky