seems like your current bioload is too much for your filtration. a refugium would definately help, if you could find room for it. they make hang-on-back style refugiums as well. perhaps upgrade to a larger skimmer if possible. reducing the bioload would help. Any one of, or all three, of these options would help. in the mean time I'd keep up with those water changes to keep things under control until the underlying issues can be addressed. I'd recommend reading here as well:
http://www.wetwebmedia.com/nitratesmar.htm
hopefully this has been helpful.