Either do meds or heat not both at once. I have made that mistake. Also it is possible to treat ich with just aquarium salt. It requires patience and time but it is doable. Also when using medication take all carbon media out of your filter. Yes that means the cartridges because they usually have carbon in them. In order to maintain some kind of mechanical filtration you can pack your filter with all kinds of different things like dollar store pot scrubbers or even lava rocks.
If the meds don't work just raise the temp to 86 degrees and do 25% daily water changes with a light gravel vac of your entire substrate. Add aquarium salt at 1 Tablespoon per 5 gallons of water if you choose too but isn't always necessary.
If you have any other fish I recommend adding some salt to help them fight the ich. I would do one teaspoon for every five gallons to start. Make sure and read your salt packaging. Aquarium salt will not magically disappear so keep good notes on how much you add and when. Also when you do a water change dose the water added not the entire tank.
It's been two days since I noticed it and that lone rummy is the only one showing any signs still though I have lost 4 others in those 2 days.
I have 1 rummy and ember tetra and 5 assorted long fin danios.
Would they be ok with temps rising to 86-89°?
Also how long after treatment should I introduce new fish?
Hoping everything goes well I'd like to get some Cory's I've had finally into the tank.
86 degrees is fine for mostly any fish short term. Generally, I continue to treat the tank for about 10 days after all signs of ick are gone. Seems to be a pretty good practice.
I know Kordon Rid ich works because I've used it for a bad case of ich in the past. But if you catch it early you really don't need meds. I usually raise the temp to 86 degrees, add aquarium salt, and change out 25% of the water daily with a light gravel vac of the entire substrate.