The bleach may kill off any adults on the plants, but won't get rid off the snail egg clutches. It's easy to miss picking off all the plant leaves that have them, too. In order to keep your plants from dying during the bleach dip, you should keep the plants submerged for only a minute or two. A couple minutes in diluted bleach won't kill every pest, so I would skip the bleach. I've tried it so many times in the past on my plants and have had negative results. I did a 1 part bleach/20 parts water ratio every time, and still ended up with a couple snails. The bleach would sometimes kill my stem plants, and with other plants would stunt their growth. I never did try alum but that may yield better results for you. There's also potassium permanganate, which I think can be found at hardware stores. Just fyi, most hitchhiking snails don't eat any kind of algae. Most of them also won't eat your plants' healthy leaves. I used to be very adamant like you are about not having ANY snails. I learned to keep their populations way under control by gravel vac'ing (which removed the detritus snails love) with every weekly water change. Get rid of them if you like, but they're not nearly as bad as most uninformed people think.
