Why no to carrots, miss Wiggle? I use that on a regular basis and have never had any problems. The only thing is, my livebearers find it a bit chewy, so it's mainly for the bristlies. I have used apple (and pear and banana) occasionally, but wouldn't do so on a regular basis, as it is a bit acid; would probably pass on the grapes for this reason.
Other veggies I use include peas (the no. 1 favourite!), courgette (zucchini), cucumber, spinach, chard, lettuce, broad beans, broccoli and (as from yesterday) pumpkin. How often depends on what fish you have: with the livebearers I feed veg three times a week, but by now most of my tanks contain a flock of hungry bristlenose juvies, so that means veggies every day.
IME boiled zucchini will sink of its own accord but cucumber won't. Boiled peas sink; I mush them up a bit so there are lots of tiny fragments for my fry. Lettuce I weigh down with bits of plant weight.
not sure if it will with larger peices though as I normally just screwcumber them, you can also squeeze them underwater and air bubbles will come out and that can help sink them when you can't find a weight.
My fish seem to prefer lettuce at the moment, I just nuke a few leaves for 30 seconds and add a plant weight at the bottom and chuck them in, the plecs/ottos are stuck to them in minutes and the rest of the fish nibble when they swim past, the Endlers love lettuce and can polish it off faster than the apple snail or the plecs.
), otherwise they just give up and don't eat them. Other fish have rasping teeth and are fine with the harder stuff. I think the fear of disintegrating food is also exaggerated; I have fry that need to eat a mushy soup of veg+infusoria, and as long as I keep up with water changes, my stats seem ok. But obviously, you don't want to leave food in until it rots.
