get a pair of surgical scissors (if you don't already have for fragging softies) and chop them down at the base/trunks and remove the trimmings. yes, many of the stumps will eventually start to grow back - but in an hour you will remove 90% of them. then, do it again the next week removing any new growth. repeat weekly as needed.
they grow fast, but not so fast that they can all grow back faster than you trim them out. and by trimming and removing you avoid a lot of the pollution that may occur with any one-shot chemical, and don't greatly disturb the tank by removing rocks.