That often means that they are even better cared for. But that also makes it very hard to give away or sell something. :)

(I remember the five living room aquariums full of our little girl's gerbils. Even I got used to saying, "Hi bear, hi hippo, hi lion, good morning giraffes, hello bears, et al" when passing through, searching for coffee, early in the morning.)

If the guppies were harassing the snail and you wanted it to survive, removing it to different quarters was wise. Maybe the snail was ailing. Maybe the guppies need some protein and would like some frozen bloodworms (defrosted in Luke-warm water and rinsed through a fine-meshed net or sieve). Maybe we have no clue why they are doing that.

Smaller pond snails certainly will do well on "left-over" aquarium food. They also forage off of plants , the gravel and glass. At a month or two after a food canister is opened, some vitamins (especially vitamin C) are supposed to have broken down. I'm trying to learn to buy differently sized packages accordingly.

Larger packages are a much better price per unit (ounce) of food. But if we feed from that for several months, there is a slightly declining benefit for the fish. The food might be better for the fish if it was used up in a month or two.

However, I often end up with some small flakes when finishing a canister. One can not get enough larger flakes out to feed the adult livebearers. Then the left-overs are dumped into a larger 7" tall food canister. That is gently stirred and fed to the snails, which don't seem to mind at all. Although fry are fed some "fresh" crushed flakes they also get a feeding from the "mix."

Some parties have suggested, especially if a person gets several sample containers in a "goody bag" (often raffle prizes at an auction or club event), mixing them in one holder. If we mixed regular flakes, some veggie flakes and a color flake package, we have "guppy flakes plus". :) That is not a bad thing and maybe the snails are doing better than the fish for the variety in their diet.

While excavating a corner of the fishroom (after an early retirement from teaching) I ran across one of those left-over canisters. It had been filled during some presidential administration other than the present one. The very aged flake residue was dumped and spaded into a a garden compost heap. The canister was rinsed and left in the recycle barrel.

Your idea of feeding snails that will give veggie eaters a little blanched piece of zucchini is a great one. (And judging from this AM's farmer's market) this is getting to the time when one can buy inexpensive zucchini. It can be microwaved for 30 seconds or a minute, left to cool and be sliced into small slices. Than it is tossed into a zip-lock bag and frozen.

The zucchini slices back-fired on me when I tossed a "zucchini coin" into a 10-gallon tank of livebearers (Gambusia vittata), a batch of growing golden bristlenose "plecos" (Ancistrus species) and too many ramshorm snails. (I'm selecting out the brown ramshorns as darter food, keeping the bright red ones). I mistakenly assumed that the assembled multitude would completely consume that slice of squash, maybe with the exception of the peel.

What they did do was tear up the slice fairly  effectively and leave it. Within a couple of hours the aquarium was horribly cloudy. Some of that may have because of the stuff passing through the animals' digestive tracts. Clearly the not-clear tank was also a mess because I overfed by adding too large a piece of zucchini.

Before keeping apple snails was a no-no, I'd put them in their own (covered) aquarium, set up for plants. Plants never got put in but the tank was well lit. The material passing through the snails fed a Kelly-green culture of protists and algae (greenwater). The apples ate everything!

Start small with your snails, maybe feeding what you think is too little. In 50-gallon breeder tanks, I've seen guys run a large stainless steel screw through a hunk of uncooked zucchini and just drop it in and let "a lot" of guppies and bristlenoses attack it. Evidently the uncooked food didn't fall apart as quickly, the number of customers was more appropriate and the larger filtration system was more effective.

Read a marine aquarium article a little while ago. It suggested that many kinds of lettuce have so little nutritional content that the fish eating it actually will lose weight by the time they have digested it. Unless you are feeding romaine lettuce (perhaps), don't bother with it, even if the fish are taking it.

A piece of wilted lettuce (washed to get rid of anything on it) is a useful "snail trap" if left in the aquarium for a few minutes. It isn't really a nutritional item in that instance though.