I live in Romania, that already says just how badly stuff is around here...Right... I think we need to step back a little...
Firstly, where are you? There might be a local forum member who could help out.
Secondly, could you describe exactly what you do when you change water/clean the tank etc.
Thirdly, what stuff do you have ie, filter, heater, etc.
Once you've told us those things we can advise you properly sound ok?
When I change the water, here's what I do:
1 - take out the fish: for the swordtails I use a net, but for the catfish I have to take him out by hand, as a net would get his fins tangled. He jumps in my hand by himself so that's easy.
2 - put the fish into some bowls covered with some plastic lid with holes (I put the hoplo separately, cause he will probably annoy the other fish in the bowl).
3 - I carry the aquarium to the bathroom, throw away ALL the old water and disinfect it with some detergent and then wash it all and wipe the tank so that it won't be wet underneath when I place it back on the stand.
4 - take tank back to stand, put the new water (which has been left outside for 2-3 days so that it won't hurt the fish, it is water from the sinks) in and then put the fish in it.
I have two filters, I use none of them anymore as I've observed no difference: the first one makes a lot of noise and blows bubbles, I don't even remember what that one looks like.
Second one has this sponge filter, but the sponge is INSIDE the tank and will just carry all the food over it. It sucks in the water and then throws it back in on the other end.
The water still needed to be changed once every 4 days back then (I fed the fish live food, but now I just buy frozen food and flakes, seems to work better).
No heating inside the aquarium, the house is heated instead, so temp is about 18-25C winter, 25-35C summer.
So I need a good filter, but what type should I get? What do you do when you need to keep your tank clean? How often do you change the water and how? I change it only when I see it start to get a bit foggy (which is either 4 days to a week depending on the food / fish mood).