Increase the water movement, especially at the surface.
Ich can get in the gills, compromising the breathing, and warmer water holds less oxygen.
Ich has a life cycle that is pretty regimented in terms of time. If things do not happen quickly for them they die. They do not have a resting, dormant or spore stage.
~On the fish: They land as single celled organisms, burrow in and start dividing. Several days to a week at tropical temperatures, a month or longer in a pond.
~Falls off fish, lands mostly on the substrate, but can also perch on other horizontal surfaces like leaves, rocks and driftwood. This is the phase that is reproducing, and some meds seem to have some affect on this phase. A day or two at tropical temperatures, several days to a week at pond temperatures.
~The reproductive form releases hundreds or more single cell babies. These drift in the water and must find a host quickly or they die. This is the phase that is most sensitive to medications, including salt. At tropical temperatures they can die as fast as 24 hours, but in a mild pond they can live for several days.
Treatments are aimed at breaking that cycle, or killing the most vulnerable phase, the drifting babies.
~Bare bottom tank, 100% water change every 24 hours. (or move the fish back and forth between 2 or more tanks). This interrupts the life cycle. The adults fall off the fish, but before they can reproduce the fish are moved and the water (with the adult Ich) is tossed out.
~Salt and heat: High temperature speeds up the life cycle so the treatment is over sooner. Salt dehydrates the baby Ich organisms. Most varieties of Ich cannot live if the temperature is over 86*F, but to be sure the WHOLE water volume is that warm, including under the substrate, you might need to raise the temperature to 90*F. This is very hard on the fish. Salt without heat also works. Maintain the tank at the best possible temperature for the fish. This will usually mean the treatment goes on longer.
~Playing games with the temperature. Ich seems to fall off the fish when the temperature is raised and lowered. This can be stressful to the fish. If you are interested in this method, do some more research. The timing and the exact temperatures are important to make this method work.
~Ultra Violet Sterilizer can be added to any of these. It will kill the babies that pass through it, so make sure circulation in the tank is optimal, and you are using the right pump to send the water through the UV.
There are several over the counter medicines available. Do not use UV with them. If you use Amquel or Amquel Plus dechlor, read the label. It should not be used with dye based medicines.
Rid Ich is one of the gentler ones.
Many meds are dye based. They often stain the silicone.
There are some pretty strong meds, quite stressful to the fish, but if the fish are in good shape, and are not delicate fish to begin with, then you could try something like Clout.
Any medicine that promises a cure in less than 2 weeks is lying. Look at Ich life cycle, the timing of each phase. Give each phase at least 10% plus or minus in the timing. Ich that is burrowed in under the slime coat of the fish is not affected by medicines. Since this phase lasts at least several days, and more often a week, there is no way a medicine will affect these in just a few days. These must fall off the fish and reproduce and it is the babies that are killed. The medicine must remain in the water the whole time, and usually a minimum of 2 weeks at tropical temperatures to be sure you have killed ALL the Ich.
There are some meds that say they are from organic materials. The posts I have seen from people who have used these are not encouraging.
Points to remember:
Ich gets on the fish a few days before you see it. When you start treatment the fish already have some 'invisible' Ich that continues to grow. So, a few days into the treatment you will continue to see more Ich showing up on the fish. This does not mean the treatment is not working.
If more spots show up after those first few days, then worry that the medicine is not killing the baby Ich organisms.
The cleaner the tank the better. Many medications act by latching onto almost any organic matter, including waste that is decomposing in the gravel. Remove all that so the medicine will attach to the Ich organisms, and improve conditions for the fish. (Salt does not work this way, but the cleaning of the bottom is improving conditions for the fish, and removing a lot of the breeding Ich.)
Fish under stress cannot osmoregulate as well as healthy fish. If you are not already doing the heat and salt method, then add some salt to the water to help reduce this stress. 1 teaspoon per 10 gallons is enough, is a mild dose that is fine with plants and delicate fish.
Ich comes from somewhere. Not the air. Not a dormant phase.
There may be a low level infection in the tank, with Ich possibly living in the gills, or an odd Ich or two somewhat hidden under a fin, or by chance on a fish that just does not turn around, so you miss it.
Ich is rampant in hatcheries, wholesalers and retailers. Assume the water in the bag has Ich, even if the fish look clear of the parasite. Assume the fish have that single cell stage before you can see it, or has some Ich hidden in the gills. QUARANTINE ALL NEW FISH, NO EXCEPTIONS.
Ich can be starved out. A couple of weeks in a tank with no host and most of the Ich is dead. I would give it a month, just to be sure, but moving the fish to a bare bottom hospital tank and leaving the main tank TOTALLY empty of fish will clean up the main tank. (Maintain the nitrifying bacteria will ammonia like you are doing the fishless cycle).