Angels Are Sick!

First off, I am a newbie so go easy on me. I have had tanks before but this is my first one in about 15 years. The tank has been up for about a month now. I first introduced two angels and four snails, two black and two gold. The angels were scared at first but then warmed up after a day or two and were eating fine. I then introduced a Bala shark and a Pictus Cat a week later. Within three days the shark was dead from what seemed to be punishment brought by the cat which was swimming around like it was insane, smashing into the glass and everything else in its way. Maybe this was an isolated event or I just made a mistake by purchasing the cat to begin with. One weeklater and now the cat is dead from what lookslike an attack from the angels, I noticed them hitting the cat every once in a while. It had a spot on its side that had a large fuzzy growth on it when it died. Now both of my angels have white fuzzy fins and I think 2 of my snails are dead, it seems very obvious that there is an infection in the tank, most likely bacterial from what I have read on here, and now that I have only my angels left I feel I should treat the whole tank because I would like to save them at least. I wish I had found this site before I started my new tank, there is an abundance of info on here. Any advice will be much appreciated, and remember I am new, so be gentle.Here is a good angle where you can see the fuzz.

Pablo 20 gal with gravel and powerfilter.

P.S.
How can you tell if a snail is dead?

White cotton, is a bacterial disease. Try to get melafix, and adding aquarium salt helps them heal faster. Did you cycle the tank? 20 gallons is almost 2 small for 2 angels, let alone anything else, you might be able to add some guppies, but nothing else. How tall is the tank? Hope this helps!!!!!!!!!!!! Welcome to the forums!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

More than likely bacterial, if you are from the US, Maracyn & Maracyn II are the most comonly available antibiotics, and can be used together. Clean water is essential as well, please fill this out, as this info will help us help you. If you have your lfs test the water, have them write down the numbers, fine describes good looking women, not water parameters.

Tank size:
pH:
ammonia:
nitrite:
nitrate:
kH:
gH:
tank temp:

Fish Symptoms (include full description including lesion, color, location, fish behavior):

Volume and Frequency of water changes:

Chemical Additives or Media in your tank:

Tank inhabitants:

Recent additions to your tank (living or decoration):

Exposure to chemicals:

Digital photo (include if possible):

Wow!! Thanx for the warm welcome!! I went and bought a master test kit, which I obviously should have done before hand.:stupid: live and learn. I have removed all carbon filtration from the tank so as not to deplete the meds and started my first treatment of Melafix, which was at 6:00p.m. It is now 11:30p.m. and the fuzz is already gone from my white Angel but my spotted has a 4 in. turd hangin from the bung, is that normal? I am currently running without any filtration for the night, I hope that is alright. I am dissolving some salt to add as well and will test the water when I get home tomorrow from work and see where we are. Both angels are swimming around and have had a nice dinner Thank you for your advice. Peace out girlscout.
Pablo