Oh dear
Where to start....
I'm sorry to tell you but it sounds like you are already several paces down the wrong road.
I'm presuming from what you have said that you have not cycled the tank at all before putting the fish in? This is not unusual, but will make things difficult for you and give you a lot of work from this point on for the few weeks certainly.
What capacity is the tank, and what filtration are you running?
The food on the bottom is a bad sign of severly overfeeding, which is something you REALLY want to avoid right now.
You will need to get yourself a decent liquid test kit, the one most commonly used on here is the API Freshwater Master Test Kit.
Also if you do not have a gravel vacuum syphon you will be wanting to get one of those.
At the moment the ammonia levels in your tank, (produced by the fish, fish waste, and decaying matter), will probably be sky high. The filter would normally remove this, but as you haven't cycled the filter the bacteria culture won't have grown in there yet, and as such at the moment the filter isn't yet doing it's job properly.
The problem with this is that Ammonia is HIGHLY toxic to the fish
My first advice is;
- Get that decaying food out of there
- Get the white fluff out of there
- Do a water change on the tank of around 50%, (making sure you add dechlorinator to the new water before you add it)
- After an hour or so do ANOTHER water change of around 50%, but keep an eye on the temperature of the tank, you don't want it to drop too much below the 25 degree C mark. The idea of these two changes is to get as much of that ammonia out of there as possible right now.
Then get the water test kit, (and gravel syphon if you don't have one). Don't be convinced by the fishshop to A) buy more fish, or B) buy any sort of bacteria helping product in a bottle.
Once you have the test kit, do the Ammonia, NitrIte, nitrAte, and ph tests on the tank, and also on your tap water and post the results back here.
You'll notice that I tend to capatalise the I in nitrIte and the A in nitrAte, that is because they are spelt very similarly, but are very different substances, and we need to be clear which one we are talking about
Sorry, but be prepared for some hard work in the coming weeks with plenty of water changes going on, will await your results