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.

 

Try Potassium permanganate it works real good. If you can't find it locally try jungle labs super clear