Ich and Raising the Temperature
Ich simply is not normally fatal in ANY aquarium with an established filter because the established filter stops the ich organism. An established filter has a whole host of tiny, microscopic organisms on the surface of the filter media which can trap and literally eat the infectious ich theront. The longer a filter has been established the better it is at “eating” the theronts.
So in a well filtered aquarium the ich usually just runs its course with no fatalities. This is the reason so many “remedies” can be found for ich. ANY remedy, including such obviously useless things like garlic, will produce success most of the time. So the anecdotal “I’ve cured ich with XXX” abounds.
Especially prevalent is the “When I raise the temperature the ich is cured”. The ich cases where this heat “cure” works are those where an established filter would have “cured” the fish with no intervention at all from the heat.
How the Myth Originated
The University of Kentucky noted that large Florida outfits which raise tropical fish by the millions have far fewer cases of ich when the water temperature goes above 85 degrees in the Florida summer. The reference is “Ich (White Spot Disease)”, Durborow et. al., University of Kentucky, 1998.
This is the ONLY reference the author could find which says raising the temperature of the water has a positive reducing effect on the ich organism. There are not even any old references which say it works.
Note that there was no clear cut “cause and effect” shown for this “fewer cases in the summer” by the University of Kentucky researchers. They HYPOTHESIZED that ich has difficulty reproducing above 85 but they gave no data or references to back it up. Any competent biologist can come up with a few dozen other possibilities as to why this occurs.
This anecdotal piece of evidence has been “morphed” into the idea that heat kills the ich organism or renders it incapable of reproducing. This simply is not a proven truth. There is no side by side experimental studies which have shown any positive effect from raising the temperature of tropical fish aquariums infested with ich. There are several side by side scientific studies with controls which show heat is NOT effective.
The best study of ich treatments was “Treatments for Ich Infestations in Channel Catfish Evaluated under Static and Flow-Through Water Conditions,” Tieman et. al. 2001. This very well done study compared ich infestations at 69 F (20.7 C), 81 F (27 C) and 85 F (29.7 C). This study found NO benefit from raising the temperature, NONE! 100% of the catfish juveniles with ich died even with 85 degree heat. Let me repeat that:
100% of the catfish juveniles with ich died even with 85 degree heat.
The author suspects the reason fish have less ich in the summer in ponds in Florida has to do more with ecology than heat. We know that there are a whole host of microscopic carnivores that “eat” free swimming ich theronts. In the summer the mass of microscopic carnivores in the algae laden water of the ponds will be much greater. Thus the infectious ich theronts have less chance of surviving to infect a fish in the summer.
Also there is one myth about raising the temperature which has to be debunked. There are several “experts” on social media who say that “most strains of ich are now resistant to the heat treatment”. Heat does not work as a cure for ich. So there is simply no good basis for saying “strains are now resistant”.
One thing raising the temperature does do is it makes the life cycle of an ich organism shorter. Since ich is normally not fatal in a filtered aquarium this leads to statements like “I raised the temperature to 86 degrees and the ich went away in four day. Normally it takes six days for ich to go away. So I know heat works“. The heat did not “work”. It did not kill the organisms or prevent them from reproducing. The heat simply caused the ich organism to fall off the fish faster.
One note on raising temperature. Raising the temperature significantly increases the oxygen needs of the fish. It both reduces the dissolved oxygen in the water, and it raises the metabolism of the fish. So the fish need more oxygen at the same time the water has less oxygen in it. The ich organism also commonly attacks the gills of the fish and reduces the ability of the fish to absorb oxygen. So raising the temperature to treat ich can kill the fish by suffocating them.
If one is treating the fish with formalin this can present an additional problem. Formalin irritates the gills of the fish and reduces the oxygen absorption capability of the gills. Heat also makes formalin more toxic and accentuates this damage to the gills. Formalin also removes oxygen from the water as it decomposes. Thus, it would is very unwise to combine high temperatures with formalin.
Belief Perseverance Effect
There are many “old dogs” in the hobby which have been using heat for many years. These “old dogs” will swear up and down that heat works to control ich and is safer than medication. They will be partially right in that heat is safer than medication.
But they will be wrong in that heat does NOT control ich. Heat will ONLY “work” if there is a well established aquarium filter because the well established filter “works”. What these “old dogs” are missing is that if one has a new aquarium with a new filter ONLY formalin/malachite green will prevent fish mortality. Trying to use an ich treatment of raising the heat on a new filter will probably result in fish mortality.
These “old dogs” will maintain their belief in heat even when presented with five or more university papers saying it doesn’t work. They will rationalize and rationalize some more and reject the scientific evidence.
This is something called “belief perseverance effect”. It says that if someone has been doing something for a long time and believes it to be effective, a normal person will rationalize and support their own beliefs. There is no point in trying to uses logic or science to change such a person’s mind, especially when a person is an “old dog”.
“Nothing dies harder than a lie that people want to believe” Calvin
Now ignoring the science and embracing the heat treatment of ich will generally not kill one’s fish. But if someone puts fish with ich in a quarantine tank with a new filter and raises the temperature the result can be a lot of dead fish. By the same process a newcomer who has ich in a new aquarium can have the same result.
Ich in more Depth
Ich is the most common fish disease and warrants a more in-depth discussion. The following chapters are devoted to this common fish disease:
10.2.2.1. Ich in More Depth
10.2.2.2. Immunity of Fish to Ich
10.2.2.3. Ich Medications
10.2.2.4. Ich Medications in More Depth
10.2.2.5. Ineffective Ich Medications
10.2.2.6. Using Filtration to Remove Ich
Return to Disease Menu
Return to Skin Protozoan Menu
Return to Ich Menu
Aquarium Science Website
The chapters shown below or on the right side in maroon lead to close to 400 articles on all aspects of keeping a freshwater aquarium. These articles have NO links to profit making sites and are thus unbiased in their recommendations, unlike all the for-profit sites you will find with Google. Bookmark and browse!