(Image Credit: Public Domain wikipedia.org/wiki/Ichthyophthirius_multifiliis)
What one of the most common diseases aquarium fish can get is Ichthyophthirius Multifiliis or Ich for short. The most difficult part of treating Ich is the fact that you have to treat the entire tank. Taking out and quarantining a couple fish that you see with white spots isn’t going to fix your problem.
The white spots (trophonts) you see on your fish is the Ich parasite that has attached itself to the host. After a time, they detach and mature into tomonts. The tomonts reproduce and create the infections tomites, which attach to your fish and starts the cycle over again.
The life cycle of Ich is largely dependent on the water temperature. At lower temperatures the life cycle slows down, at higher temperatures, it speeds up. At 77°F (25°C), the full life cycle of Ich takes about 7 days, at 50°F (10°C), it takes about a month. This time continues to shorten as temperature increases until about 85°F (29.5°C) when the Ich no longer has the ability to attach to a new host and at 86°F (30°C) when the Ich stops reproducing.
Usually, once someone sees the dreaded white spots on their fish (after the inevitable “where the hell did this come from?”), the first instinct is to go out and get medication. While this can help get rid of the Ich problem, it usually stresses your fish, or if you have scaleless fish (like loaches), you can’t use medication anyway since it will likely kill them. If you choose this method, follow the directions exactly. If misused it could harm your fish, live plants, and/or the bacterias that keep your nitrogen cycle going. Do not increase the water temperature with this method.
Another common method is a salt dip. Since freshwater Ich doesn’t like salt, so it will detach from the fish early and attempt to find better water. I find this method to be unnecessary since it adds an additional part to the method described below (heat method), and not all fish can handle salt (again, loaches). If you do choose this method, do a water change, then add aquarium salt to your tank until the specific gravity is at 1.002 g/cm3 (about 2-3 teaspoons/gallon, dissolved in warm water before adding). Once the specific gravity is at the desired level follow the directions for the method below (without the initial water change).
When I treated an Ich outbreak in my Kuhli Loach tank, I used the heat method which is, in my opinion, the safer strategy.
Most tropical fish should not have an issue with the temperature increase to 86°F (30°C). If you have a small aquarium (around 10 gallons), you won’t have any trouble keeping the temperature that high, but if your aquarium is any larger than that, it can be a struggle. To maintain the temperature in my 29 gals (110 L) bowfront, I set my heater to 89°F (31.9°C). I also used two thermometers, one on each side of the tank, to make sure that the temperature was high enough throughout.
Before you being your treatment, you’ll want to do a 50% water change, then begin increasing the temperature slowly, no more than a degree/hour (slower is better). Once you get the entire tank to 86°F (30°C), you’ll want to keep it there for about two weeks (one week if you’re using salt). This will ensure that the Ich is gone. During this time, do NOT do water changes, a water change will lower the water temperature too much, and you’ll have to start over again. After the two weeks, inspect your fish for any signs of Ich. If you still see some white spots, the temperature of the tank likely dropped too low at some point. Do a water change, increase your heat and start the two weeks over again. If the fish all look healthy, turn your heater down, do a water change, and you’re all set!