Watching videos on ich. First guy says to raise temp to 83F if fish can tolerate it, dose heavily with salt (he specified quantity & I can’t remember now) then use IchX per instructions.
This is the second vid by Cory at Aquarium Coop. I’ve seen him before & he appears credible. Sometimes he uses salt & other times not. He glosses over salt treatment & focuses on IchX. He uses IchX on all new arrivals. He said the origin of ich in a tank is controversial in that it can appear in established tanks where no new fish etc have been introduced. He said he’s seen it in tanks 6 months to 2 yrs old. He thinks big changes in params can trigger an infection. Some viewers in the comment section agree. Mostly he discussed the IchX instructions & had good graphics including photos of infected fish & diagrams of the life cycle.
Be careful about what you see in online videos, not all are accurate. The people doing the videos are often more interested in ratings than providing correct information. There are some good videos out there, but a lot of them aren't as good as they could be. A lot of people also specialise in one subject (maybe a reef tank) but know next to nothing about other fish related subjects. This is common in people keeping cichlids or plant tanks. Many claim to be experts and know a lot about their particular cichlids or plants, but very few know more than that.
Salt doesn't treat white spot but can be used to reduce the chance of secondary infections (as mentioned in the link from Andy). White spot parasites occur on fish in fresh, brackish and saltwater environments. If fish have white spot and are being treated with heat or chemical medications, they are already under stress and adding salt can increase the stress they are under. There's no need to compound the stress they are under by adding salt to a freshwater tank when it isn't going to make much, if any difference.
If you want to use salt, see below, but don't add it to a tank unless it is necessary because it can harm freshwater fishes, especially those that come from soft water habitats.
The white spot in your tank came from the fish that were recently introduced. A few parasites got into the tank and caused the outbreak. It happens to the best of us. It's happened to me and other people I know, and will keep happening because it is such a small parasite that can be easily overlooked until it builds up in numbers.
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SALT
Using Salt to Treat Fish Health Issues.
For some fish diseases you can use salt (sodium chloride) to treat the ailment rather than using a chemical based medication. Salt is relatively safe and is regularly used in the aquaculture industry to treat food fish for diseases. Salt has been successfully used to treat minor fungal and bacterial infections, as well as a number of external protozoan infections. Salt alone will not treat whitespot (Ichthyophthirius) or Velvet (Oodinium) but will treat most other types of external protozoan infections in freshwater fishes. Salt can treat early stages of hole in the head disease caused by Hexamita but it needs to be done in conjunction with cleaning up the tank. Salt can also be used to treat anchor worm (Lernaea), fish lice (Argulus), gill flukes (Dactylogyrus), skin flukes (Gyrodactylus), Epistylis, Microsporidian and Spironucleus infections.
You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres (5 gallons) of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.
If you only have livebearers (guppies, platies, swordtails, mollies), goldfish or rainbowfish in the tank you can double that dose rate, so you would add 2 heaped tablespoons per 20 litres and if there is no improvement after 48 hours, then increase it so there is a total of 4 heaped tablespoons of salt per 20 litres.
Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.
The salt will not affect the beneficial filter bacteria but the higher dose rate (4 heaped tablespoons per 20 litres) will affect some plants and some snails. The lower dose rate (1-2 heaped tablespoons per 20 litres) will not affect fish, plants, shrimp or snails.
After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.
If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.
When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.