Fallow works when the tank is empty and steps are taken such as raising temperature to kill trophants and speed the cycle. Just because dots vanish does not notate the parasite is idle. Doing this 35+ years, ive rarely seen a fish survive ich Untreated. The ocean (open environment) is no comparison to a fish aquarium in which we lack the natural diets and antibodies that disallow this condition in the wild. The cycle of ich first needs to be understood.
Marine ich has a complex multi-step life cycle.
- The feeding or trophont stage is where the parasites are swimming around under the skin and gills of the fish. The parasites eat cells and fluids, damaging tissues and leaving the fish in a weakened state. Here is where you may see the white spots and other outward symptoms. Ich treatments generally do not affect the trophonts because they are protected under the skin of the fish.
- Once the Marine Ich Trophonts are fattened up, they leave the fish as a protomont. Protomonts lose their ability to swim, fall to the bottom of the tank and in a few hours become a tomont. The parasite becomes a hardened cyst, like an ich egg, waiting to hatch. The tomont is a ticking time bomb full of nasty little parasites. What was once a single ich parasite, now divides, again and again, storing up hundreds of new parasites called tomites.
- After a number of days or even weeks, the cyst opens up and the infective parasites are released as free-swimming theronts, seeking to attack your fish.
This is really the primary stage that these medications are effective against the parasites. The theronts have about six hours to find a fish and burrow into the skin, becoming a trophont. Then the cycle begins again. Depending on the severity of the outbreak, an aquarium or shop full of marine fish can be wiped out due to the reoccurring nature of the parasite life cycle.
The theory goes that if you can avoid affecting any fish (eg. leave your fish in quarantine, under treatment for that period of time), you can add them to your tank relatively risk-free.
The best way to protect your saltwater fish tank or reef aquarium is prevention. Prevention means keeping ich-infested fish out of the aquarium. This is done with a quarantine tank. The idea behind quarantine is to isolate a new fish, observe it for several weeks, ideally one month to make sure the fish is healthy. A quarantine aquarium can be as simple as a ten, or twenty-gallon tank with a heater and filter. If it is carrying saltwater ick, a fish will likely show signs during the quarantine. If it does, your quarantine tank helps you keep from infesting your main aquarium and also provides you with a small, safe location to treat your sick fish.
@Jay Hemdal works at public aquarium and can touch further on this