The good news is that there seem to be no overnight deaths, but we really don't know much about long-term effects of an exposure to melons.
Now, the loach reaction:
One species took to it instantly:

I think all of P. Oblonga visited the melon within first ten minutes and ate with no hesitation. Striped kuhlis did not react to it at all.
Zippers were the next.
The procedure was the same with each fish: approach the melon, touch it with barbels, and leave for a couple of minutes... then come back and eat.
One of the clowns and one of the yoyo's did the same, the yoyo also tested it with barbels before eating.
Schistura, striped kuhlis, and Kubs were not interested at all.
Toxic fumes of the melon had some effect on the yoyo's who got into serious bickering...this, together with rainbows hovering low above the melon, kuhlis and zippers coming and going, and me watching produced a madhouse.
And then after watching them slowly eating for a half hour, I left for just a minute and someone ate the entire piece... no idea who...
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Did anyone try this on hillstreams ?