Nearly everyone who has owned an aquarium, freshwater or saltwater, has at one time or another had an outbreak of the parasite commonly called Ick, or White Spot. Perhaps with a little bit of background, you might gain an understanding in controlling and eliminating this parasite from your aquarium.
In freshwater applications, the parasite is Ichthyophthirius multifiliis, and in marine aquariums it is Cryptcaryon irriitans. To avoid these multiple syllable tongue twisters, we use the Ick/Ich shortcut. Both are a protozoan, a single cell organism usually too small to see. They use multiple cilia for locomotion and gathering food. These aquarium parasites multiply by simple binary fission, and their population can explode in a single life cycle. When there is an outbreak of the Ick parasite, the aquarium is infested and must be treated. The life cycle of the parasite only offers a limited timeframe for treatment. We usually notice the Ick parasite while it is attached to the skin or gill membrane of the fish and has formed a thin capsule over the parasite. The best way to describe it is that it looks like a salt crystal attached to the fish. While attached to the fish, the parasite will absorb fluids and cells to mature. Once mature, it burst from the capsule on the fish and settles in the substrate or on a solid surface and produces a gelatinous capsule and begins to divide, producing up to 1,000 new parasites. The capsule breaks open and the new parasites are in a “free swimming” life stage and begin to hunt for a host. The whole life cycle can take 4 to 7 days depending on the temperature, shorter in higher temperatures. It is during this “free swimming” stage that the parasite can be killed by treatments. Anti-parasite treatments can use formaldehyde, malachite green, or be copper-based treatments. Since none of these can be used in a reef aquarium, manufacturers have developed invertebrate safe treatments. The key is to follow through with the treatment for at least 5 days after you have seen cysts on the fish. You can also kill the parasite by raising the temperature to 90°F for 3 to 7 days, if the fish can tolerate that high of a temperature.
Now that we have discussed treatments, it is time to talk about prevention of this parasite. Just like every book you have ever read about maintaining aquariums, the simple answer is to use a quarantine tank for all new fish, and, if need be, treat them before they are added to the display aquarium. This tank does not to be too elaborate. Depending on the fish, you can use a 5 gallon bucket, 10-20 gallon aquarium or even a plastic storage container. Fill this tank with water from the display aquarium (put the new water in the display tank, it probably needs a water change) and use a small filter to circulate the water. If you plan to use a treatment it would be best not to use chemical media or a substrate that might absorb some of the medication. Air driven sponge filters are popular filters to use in these situations. If you have a sump filter, you can even mature the sponge filter by placing it in the sump for use on demand. Once used in the quarantine tank, give the sponge a Clorox treatment before placing it back in the sump for use again at a later time. Proper treatment in a quarantine system can eliminate over 99% of the display tank infestations. The ich treatments are also much more successful, but in all cases, it is important to treat as soon as the parasite is seen on a fish. I am sure you see this quote coming: “an ounce of prevention is worth a pound of cure”.