is it possible to separate your chocolate gouramis?
Keep them in a separate hospital tank for both treatment, as well as permanent housing.
I find them too sensitive for community tanks - And in your case, they can jeopardize the health of your other fish.
If you cannot separate them, I completely understand.
Now to begin, is your tank completely cycled?
Treating ick in an uncycled tank is a losing battle, since you have an underlying problem that will cause further stress to the fish (if it hasn't already)
so to treating ick....
The Ich life cycle is temperature dependent. Higher temperatures within its livable range speed up every stage of the life cycle, while the lower temperatures will slow it down. At 18°C/64°F the cycle takes 10-12 days to complete.
It has been found that Ich does not infect new fish at 29.4°C/85°F (Johnson, 1976), stops reproducing at 30°C/86°F (Dr. Nick St. Erne, DVM, pers. comm.), and dies at 32°C/89.5°F (Meyer, 1984) -
sorry I had to include the 'science' for some folks
Treatment
Now that we know a little more about Ich, we can develop a safe and effective natural treatment plan to eradicate it. A multi-pronged treatment plan offers the most assurance of complete eradication of Ich and TLC for the fishes in your aquarium. As with any treatment, carefully observe the reaction of your fish to any changes you make in their environment. If an adverse reaction occurs, discontinue and try another approach.
1. Increase temperature to 30°C/86°F. With tropical fish, an increase in temperature to 30°C/86°F is usually very well-tolerated. Since this temperature prevents reproduction of Ich, it can theoretically cure the problem by itself. So the first step would be to increase the temperature slowly, 1°C/2°F per hour until the correct temperature is reached. This temperature should be maintained for 10 days, and then slowly returned to normal. Some fish can tolerate higher temperatures. If your fish are more heat tolerant, try increasing the temperature to 32°C/89.5°F for the first 3-4 days to kill the Ich. Then reduce temperature slowly to 30°C/86°F, and hold it there for an additional 6-7 days, or until a total of 10 days have passed. Gauge the heat tolerance of your fish by observing their reaction.
2. Increase aeration. Increased temperature leads to increased metabolism, which enhances the fish’s immune response but also increases oxygen demand. Oxygen is lower in warmer water, so it is very important to increase surface agitation during the treatment to increase oxygenation. In planted tanks with CO2 injection, the CO2 should be turned off and extra aeration should be provided. Carefully observe your fish, watching for signs that they are not getting enough oxygen. If fish are gasping at the surface, you need to provide more aeration. Aeration can be increased by reducing the water level so the filter return makes more of a waterfall and splash, and/or use an airstone placed close to the surface of the water.
3. Do daily partial water changes. 25% daily partial water changes will provide several benefits: It will keep the water very clean, which will help fish cope with the stress of the disease. It will remove some of the trophonts and tomites. It will add oxygen. If the water changes seem to stress the fish, reduce the size and/or frequency of the water changes.