I had nothing but trouble with this plant everytime I had them they did the same thing to me.
And the main thing with these guys is that they like CO2 in there tank.....Check this out!
"The Cabomba, also known as the Carolina Fanwort, has feathery green leaves, which are divided into narrow segments. It is a densely growing plant that makes for a wonderfull, natural looking background in a planted aquarium.
Cabomba does best when grown in nuetral water under moderate lighting. Provide at least 2 watts per gallon of full spectrum (5000-7000K) lighting. Water temperature between 72°-82°F, an alkalinity of 3-8 dKH and a pH of 6.5-7.5 is ideal for proper growth. These plants do not tolerate frequent trimming and transplanting. Leaves dropping from the plant are usually a sign of poor water conditions or CO2 deficiency.
Propagate the Cabomba by trimming branches from the main plant, and relocating them in another part of the aquarium. It should be placed in the back or sides of your aquarium in groups for the best appearance. "
http://www.liveaquaria.com/product/prod_Di...d=26&pCatId=796