I'm a bit surprised that they took off in only 5 days, as I have always found Valonia to be fairly slow developing. I just remove them by hand--you need to grab them at the base and sometimes get them out of small crevices. If any are large (~1/4 inch) be especially careful not to pop them as they may be mature enought to contain spores. If you have more than a few dozen, you might try Emerald crabs. Here's a further link. I have not tried his method.
http://home.ptd.net/~reef101/phosrep.htm