Don't jump into conclusion that fish is infected with diseases or parasites.
From your previous threads, we have learned that your fish are living in less than ideal, undersized, uncycled fish tank.
A single wet spot doesn't mean ich. If the fish has multiple of such white spots, then it can be ich. Only with a good photo we can tell for sure. Yes, ich is very contagious. Even if other fish in the same tank seem to be uneffected, ich parasites can hide in the gill.
You told us you just bought a slightly bigger tank, the 8.5 gallon. Why not transfer the fish into there? Fishless cycle can take up to 6~8 weeks to completely. Your fish won't be able to make it that long in the smaller tank. The bigger tank can't guarantee them to survive since it is not cycled yet, but the fish will have a better chance in there since both tanks are uncycled.
