Hi Cran,
I wouldn’t give up on fish for good just yet. They are a real pleasure, and very relaxing to watch.
You should set up the aquarium, with an air bubbler if possible (though these can be noisy in a bedroom), to acclimatise for at least a week, and preferably two, before introducing any fish. Decholrination additives should be used when you set it up, not added to the water once the fish are in.
Every week, you should change 10% of the water in the tank. Set aside the correct volume of water, add the de-chlorinator, cover to stop dust and dirt getting in, and leave overnight to acclimatise. Then remove 10% of the aquarium water, preferably by syphoning out with a plastic tube from the bottom. This will help remove fish poo, uneated food, and bits of gunk from the bottom of the tank. Top the tank up again using the water you have prepared, carefully so as not to stir up too much bottom gunk still remaining.
A fish can be a companion for years, if you are lucky.
Now a fish tale. A year or so ago I bought nine goldfish of various sorts, making sure their combined length was appropriate for the size of my tank. Within a week, four had died. The remaining five lived happily for over many months (and sevela long absences of me, living on holiday feed blocks) until this summer, when I noticed that one had a bit of whitespot on his nose. I bought some whitespot medicine, and added a measure to the tank. Sadly I read the tiny print instructions wrong, and added 10x too much. By the morning I had five ailing fish. The basic “no frills” goldfish lasted the longest, but sadly I had poisoned the water too much, and none survived.
You should look closely at fish at least once a week, and at the first sign of illness (usually a visible growth on the scales) add the correct medicine in the correct dosage. Too little is safer than too much.
Also, I wouldn’t advise putting ivy or other land based plants in the tank, just fishweed bought at a store for the purpose.