An alternate view from Snorvich.....
Leave it alone. Try this; Figure out the cubic inches of water volume in a 300 gallon tank (~50,000 cu. in.) and then figure that a trophont or tomite or whatever is about .000000008 cubic inches. It is reasonable to assume that with the number (volume) of fish in your tank, the majority of these tiny little critters will float around in their 12 hour life cycle without finding a host and will end up dying. Even if they do find a host, you ARE keeping your water quality pristine and making sure that your fish are well fed and otherwise healthy, right?
Don't panic, there is a good chance that your fish will fight this off and in a 300 gallon tank the ich will burn itself out within a matter of a week or two.