sounds like you maybe got some planeria or something.
a weak bleach solution, 19 parts water to 1 part bleach, will kill snail eggs, algae spores and any other nasties. You only wanna dip for a minute or two at the most. Any very fine leaved 'pinnate' plants (cabomba, ambulia, etc) should literally only be dipped 15-30 seconds, or you risk killing the plant.
If you can get some potassium permangenate, it's milder and will get the same thing accomplished. Usually this can be found at Sears or Home Depot like places, near their humidifiers. its used as some kind of humidifier cleaner. I'm not sure on the ratio to mix with water though.