More than just a bit. At the very least, try to rehome the CAE. It's got the largest adult size out of the bunch by a good margin and as they grow, they turn aggressive. People have had them do damage in far larger tanks, particularly to slow moving fish like gouramis, but in such a confined area, it'll be a real terror, since even the more nimble fish won't have room to get away. I'd also advise trading in the rainbowfish - if you want something similar, dwarf neon rainbows have a similar look in a package about a third the size (a bit bigger than neon tetras full grown). The rest, I think could be managed. Not ideal for the gourami, but they're not highly active fish, so maybe, provided excellent water quality.
The barbs probably just taste something on the shell or are looking for food, nothing to worry about there, but monitor your pH. Most saltwater shells will dissolve in fresh water. In a small tank, it might cause a pH fluctuation, but chances are it'll just start to look ragged over time. Depending on how close you are to the beach, you can always just toss it and go find a new one when that starts to happen.
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)but I got the Barbs from a friend, and I try to take really good care of the water.
