1) veggies are great! I feed mine boiled zuccini. I leave it in for 12hours so it foesnt mess up my water. Try boiling the lettuce it should sink then, but it will become mushy, your snail wont care. You can also get food clips at your LFS
to keep stuff down.
2) no bleach! sheesh, who ever told you that! I have heard for cleaning decorations but not on a living thing. A soft bristle toothbrush might work but kep him in water while you do it, just scoop a bowl of it out of your tank. Also, don't scrub very hard. Personally, i would leave the algea, but that is just me.
3)Take out the plants and rinse in warm water
hope this helps. Good luck