The problem with the pre-filters is that they don't get all of the heavies, just the easy crap..That's why R/O membranes were developed...I'd stick with R/O since we're talking wild strains...JMO, but I have tried just prefiltering, and it didn't give me the results I was seeking...R/O, R/O, R/O your boat, gently down the stream....there's a lot more R/O users than you might think, but many are still in the closet 'cuz they can't take the flack....Gary