whenever i come near to my tank and eating something,
i used to throw a chip in it: banana, orange, apple,
lettuce, celery stalk, cornicks, chippy, etc, etc.
i just scope anything left behind un-eaten. most of
the time, the first 6 items were consumed.
i believe it will not harm your fish to throw in
something and just make sure to removed those unconsume
later.