there are these nudibranchs on my colt coral about the size of a pencil eraser and light brown in color. My colt has been sagging all day until I blew the slugs off now its still not looking great. Are they something to worry about? Can I get rid of them? They swim with an undulating motion if that helps.

I guarantee they are eating your leather. If you have other similar corals they could be in trouble as well. If it were me, I would remove all the leathers to QT, treat them to kill the present nudis and let the ones still in the display starve.... but I know most peeps won't do that.

If you put 8 drops of salifert exit in 3 gallons of saltwater and dip the colt for 15 minutes, it will kill the present nudis. It won't do anything for the eggs which will need to be removed manual... inspect the coral well. And it won't do anything for the nudis in the display tank that will crawl back on. At the end of 15 minutes shake the coral in the solution vigourly. Then place in clean SW for 15 minutes more and then return to wherever you choose to return it too.