Do daily or at the least every other day water changes that emphasize gravel vacs.
Dose per label direction which ever meds you have chosen to use.
Do not run UV with any meds. Many meds are broken down when exposed to light, and UV is very strong light.
Increase aeration in the tank. You might do this with a bubbler, or allow the water level to drop a bit so water returning from the filter splashes a bit, and certainly making sure the power heads are running properly is important.
The usual course of Ich:
Ich arrives in the tank, and you cannot see it. May be hidden in the gills of the new fish, or just attached to the fish and still a single cell, so you cannot see it.
Ich grows, falls off the fish and reproduces. This may take a few days if the Ich just got on the fish in the store, or it might happen right when you add the fish to the tank. The shock of the water change (from store to home water) might make the Ich fall off. Ich babies may also have been swimming in the water from the store. So, even at the beginning there may be Ich in several stages introduced to your tank.
Ich babies land on the original fish in the tank. You do not see much for a day or two, but as the Ich grows and the fish is irritated you see white spots and flashing. As several days go by you see more and more white spots show up on the fish. These are Ich that landed on the fish a few days ago, when they were too small to see, and have been growing.
When you add medicine you are killing the babies that swim in the water. Any Ich that is on the fish are covered with the fish's slime coat, and are not killed. You will continue to see new spots show up for a few days after you start medicines. Remember Ich lands on the fish and is too small to see for a few days.
However, to continue to see more and more spots after the first few days of medication (say a week at the most) suggests the medicine is not killing the baby Ich.
Your UV is not working, or the Ich is not getting pumped through the UV, and the medicine might be getting broken down by the UV. This is not a contradiction in terms: The bulb might be weakening in the UV. It might be strong enough to affect the medicine, but not enough to kill Ich. Or, the water from every corner of the tank is not passing though the UV often enough. Baby Ich is finding its way to the fish before getting killed by the UV.
Here is what I would do:
1) Separate the fish according to how high a temperature they can tolerate.
2) Put them in bare bottom tanks. High water flow, a rock or two, live plants are OK floating in the water, not on the floor of the tank. Split the filter media the same way you split the fish: If 75% of the fish are in the warm water, then put 75% of the filter media in that tank. The filter media has a lot of nitrifying bacteria and both tanks will need these bacteria.
3) Increase the temperature in the tanks to the maximum the fish can handle. Higher than 86*F for the 'warm water' fish.
Perhaps upper 70s, or at least mid 70s for the cool water fish. You can raise the temperature pretty fast, a couple of degrees a day, easily, perhaps faster. If the fish are stressed for oxygen (poor gill efficiency because of Ich in the gills, and warm water holds less oxygen) then increase the surface movement of the water to raise the oxygen level.
4) Add UV to both tanks. Get a new bulb for the one you have, (Unless the bulb is less than 1 year old) and make sure the UV is rated for a larger tank than you are using it on. Make sure to set up the water circulation so it all passes through the UV. Check the manufacturer for proper flow rate to kill Ich. It varies. If the water passes through too fast Ich is not killed.
5) Add salt. A little each day until you have the full dose in the tanks.
For fish that are tolerant of salt: Add 1 teaspoon per 5 gallons every day for 3 days. Total dose is 1 tablespoon per 5 gallons. This may be so much the plants do not like it and die. Plastic plants are OK to provide hiding places for the fish.
For fish that are not very tolerant of salt: Add 1 teaspoon per 10 gallons every day for 3 days. Total dose is 1 tablespoon per 10 gallons. Some plants might handle this.
6) Daily water changes that emphasize vacuuming the floor of the tank. Ich will land mostly on the floor, but also on the rocks that are there for the fish to hide among. Move the rocks and vacuum under them every time. Add salt to the new water equal to the concentration in the tank.
Continue treatment until at least 3 days in the warm tank, and a week in the cool tank has passed since you last saw any Ich. Do not drop the salt level right away with one big water change. Do weekly or twice weekly water changes of about 25% with no salt added. This will drop the salt level slowly over a period of about a month so the fish can adjust.
26 tanks, over 3000 liters of water to keep clean and fresh.
Happy fish keeping!