You can use a bleach dip, but there's a risk it can kill the plants, too. I have used it successfully, though, without killing them. The following is the how-to (about killing snails, though it only mentions algae here) from aquariumplants.com:
leach (Chlorine) Dip
This is a more effective and sure-fire way to kill algae. It is also very easy to kill the plant in the process. Regular household bleach (i.e. Clorox) is diluted to a 5% (19 parts water to 1 part bleach) solution in a bucket. It's good to have a second bucket filled with rinse water containing 3X the normal dechlor. Dip large leaf plants for 3 minutes, immediately move to the dechlor rinse water, then rinse under running tap water for a few seconds, if you still smell chlorine, repeat the rinse process again. For small delicate leaf plants and mosses dip for only 2 minutes in the bleach. To be safe, add dechlor to the tank after adding the plants back. Also, if your dipping a lot of plants you may need to add more dechlor to your rinse water.