I will start with the 2 most common illness's: ich(white spots) and swim bladder disease.-both I have had experience with. If you do not have these two look at this link: http://www.my-tropical-fish.com/ click on the "diseases" tab.
Ich- or white spots disease
It looks like salt is sprinkled on your fish. It is present in the tank at all times but it is when it is visible it gets deathly.-you need to treat it.
The first time my fish had ich I tried a store treatment.-it did not work and all my fish died. Once I got rid of the ich(by not having any fish in it for a long time) I restocked my tank. In a couple of weeks I noticed it. You should look at your fish every day; and see if you notice these "white spots".-or simply strange behavior.
This is a pic of a fish with BAD ich: http://www.google.com/imgres?hl=en&client=firefox-a&hs=f8U&rls=org.mozilla:en-US:official&biw=1013&bih=602&tbm=isch&tbnid=1UZu9-evLVtwRM:&imgrefurl=http://www.bettainfo.com/ich-ick&imgurl=http://www.bettainfo.com/wp-content/uploads/betta-fish-ich.jpg&w=696&h=522&ei=VZ05UJu7Gcn9iwKE24HQDw&zoom=1&iact=rc&dur=247&sig=105757475644895236426&page=1&tbnh=127&tbnw=158&start=0&ndsp=17&ved=1t:429,r:5,s:0,i:88&tx=57&ty=49
And good ich: No just kidding a "light case" of ich: http://www.google.com/imgres?hl=en&client=firefox-a&hs=f8U&rls=org.mozilla:en-US:official&biw=1013&bih=602&tbm=isch&tbnid=PixrQmt8iM-33M:&imgrefurl=http://www.aboutfishonline.com/articles/ich.html&imgurl=http://www.aboutfishonline.com/images/ich.jpg&w=500&h=375&ei=VZ05UJu7Gcn9iwKE24HQDw&zoom=1&iact=hc&vpx=108&vpy=283&dur=669&hovh=194&hovw=259&tx=155&ty=111&sig=105757475644895236426&page=1&tbnh=123&tbnw=194&start=0&ndsp=17&ved=1t:429,r:6,s:0,i:92
Anyway, we live an hour away from town so store treatment was a "no".
I looked online for a remedy. This is what I did:
I put 2 Tablespoons of salt in(1 tablespoon for every 5 gallons).
This part is very important.
You CAN NOT use table salt being as iodine is extremely toxic to fish(it can kill them). I used kosher salt. But you can also use aquarium salt, pickling salt and sea salt with out anti caking agents. If you noticed the ich pretty late you may want to put a bit more salt in. Some say salt is toxic to some fish.-I do not know if this is true but your fish WILL die if you do not treat them. Salt also helps with stress(ich is stressful on fish). I put it in(same amount) when my fish are looking a bit down.
Now here is the important part:
DO NOT have your tank at 80-82 degrees. Ich grow the fastest at those temperatures(they have a bunch of offspring).
Ich can not survive over 85 degrees. So put it at 86 degrees. Make sure your thermometer is on the opposite side of the tank as your heater. You may want to do a water change.
If your fish get better in less than 1 and a half weeks leave it at that temperature for 2 weeks.(NO MATTER WHAT!) If more(it probably will be) turn it to the regular temp 4 days after ALL signs of ich are gone.
You may have looked up if some of your fish can handle this temp. This is the part that really KILLS the ich.-Do it. I found that what they say the "maximum temp" is wrong.
You have 2 options:
1: Have all fish die.
2: Have none or some fish die.
