Just as Gina said. Vanquish's thread has some good info on how he caught them. He used an hour glass shaped glass to do it. they go in to getthe food but can't get out once in. Seems like a good idea to me. The reason why your plants are dieing is most likely the lighting imo. They could be getting burned out. And the water quality is very good. I see no growth from picture to picture. these plants feed on fish poop and such. How much water changes are you doing a week? this could be another reason. Your keeping the water clean.
not a bad thing for a reef! Try focusing on corals instead of plants. you would do very well i think. Besides...... those plants could take over a tank if you let them.