I would like to add a sediment pre-filter and a carbon post-filter before/after the softener and Filox filter tank. Any recommendations on good models to consider? Originally we bought the Crystal Quest 20" canisters but they are having manufacturing problems with their thread machining, and so we had to return them. I noticed that most of the filter canisters out there are pretty small. I'm looking for larger-than-average ones for less flow restriction, and preferably in stainless steel but might consider plastic too.