I would treat as columnaris, as this is the faster moving of the two diseases. Carbon in the filter has been implicated in HITH in some research. If you are running carbon you will be removing it if you med. Metronidazole works really well on the internal form of heximita, many people have helped New World cichlids with HITH by feeding a vitamin enriched diet, along with frequent water changes.
Here lies one of the biggest problems with sick fish, med availability. Metronidazole is available at most any lfs here, I think you will have to go to a vet to get it, or dimetronidazole. As far as enriching with vitamins, get a liquid vitamin, the type often used for infants or children. Soak a few pellets in a few drops of vitamin, and feed to the fish. Just make sure the vitamins contain no alcohol, they used to years ago here. If you go the vitamin route, you can start treating for HITH along with treating for columnaris.