I found the replacements on their website
P U R E W A T E R C L U B
The page isnt linking right I don't think... but all four filters are $54!!!!
I think early next year I may have to replace some since my water consumption is pretty low at that time if I'm still going fish strong I may just buy a regular sized unit and actually hook it up to a permanent water supply.
$54 is outraegous! Not sure of the ones on eBay I wasn't sure which one was a direct replacement.