Quarantine prior to display placement is always ideal to isolate pests and disease in a system set up for treatment as apposed to a system that cannot be treated without negatively impacting health of inverts and other livestock. Not all fish can be treated with copper for example as some are sensitive to it.
When treating ich it is first important to understand the lifecycle of this parasite.
Stage 1. Trophont:
This is the stage where you see classic symptoms: white spots (like salt grains) on the fish's skin and gills. The parasite digs under the fish's skin to feed on it. During this time, they are deeply embedded and fully protected from medications by the skin and slime coat.
Stage 2. Tomont:
Once mature, the parasite drops from the fish and settles into the substrate. It forms a hard, sticky, protective cyst around itself. Inside this cyst, it divides into hundreds of new parasites called tomites. Like the trophont stage, the parasite is immune to medications here protected by the cyst.
3. Theront:
The cyst opens, releasing hundreds to thousands of free-swimming parasites into the water. These theronts ravenously seek out a new fish host to feed from. This is the only stage where the parasite is vulnerable to medical treatments in the water column. They only have about 48 to 72 hours in this stage to find a host. If they do not find a host to latch onto, they die.
This can vary with temperature fluctuations speeding up in warmer water and slowing in colder water. UV is helpful in the last stage of Ichs lifecyle and this is when treatments are most effective as well. Copper will work for some species but may prove lethal to others.
Chloroquine phosphate is alo effective but cannot be reliably measured by home aquarists. Hypoaalinity is effective to a degree, increased temperature along with uv sterilization is also effective to a degree. Formaldehyde based treatments have also proven effective over the years. Always use caution when handling these chemicals as there are consequences to exposure. Beyond this there is a method known as the tank transfer method and fallow system operation. I can dive deeper into these if anyone is interested.
Another thing to consider that is often overlooked by hobbyists and public institutions is the occurrence of secondary infections prevalent in fish populations effected by parasites. Open wounds are a fantastic entry point for bacteria and often times lead to secondary infections. Using a blend of metronidazole (seachem metroplex) combined with an antibacterial polymer such as (seachem focus) can help treat minor secondary infections. This blend of medication can be soaked into food to offer the fish systemic protection and treatment from infection as they are treated and healing. This should help the majority of hobbyists. To help entice fish to feed, garlic juice can be added to foods as an appetite stimulant. Vitamins and amino acids should also be considered to improve nutrition for animals that may be lacking due to irritation preventing normal consumption levels. Focus on nutrition is also a great preventive measure for fish disease.
More severe infections may require more intense antibiotic treatments and can be covered separately as there is a range of infectious bacteria species and treatments specific to each group.
