I've used the KX line
of extruded carbon filters for many years in 'technical' and biological filtration applications. Good products.
I currently have a KX carbon 'prefilter' for my boat system .... for attachment to a dock hose and my 1,0ÁM 'absolute' cyst filter .... for tank filling.
KX are well made, they are standard 'industrial' configuration 2.5"ě X 10" (for 9-3/4" filters use 2pcs. - 1/4" gaskets on each end of the filter for use in a 10" housing) - important so you are not committed to use an expensive 'proprietary configuration' filter from solely one supplier, etc.
To get the best adsorption results (from any carbon packed filter) you should flow the water through carbon filters 'as slow as possible' as adsorption is dependent on 'dwell time' inside the filter media. I recommend that carbon filters NOT be placed IN a boats water distribution system ... 1. removes the needed chlorine from the system water (even when there is no water flowing); 2. the carbon is a nutrient source for many microorganisms. I recommend that you use them on the 'charging hose' delivering into a 'clean and sanitized' tankage.
The downside .... the micron rating is 'nominal' or arbitrary so that 5ÁM can theoretically pass ~50ÁM particles and you should have a 'more accurate' filter immediately downstream. For precise filtration, especially to exclude dangerous and chlorine resistant 'cysts', etc. you need a filter that is 'rated' for: 1,2ÁM 'absolute' or 1,2ÁM 99% or "FDA/NSF rated for oocyst removal', etc.
Before I installed a RO system and used to catch water, use 'cistern water', or water from 'unknown' ... I had a 5 gallon 'pre-tank' that was easily fillable. I pressure filtered from the 'pre-tank' to the 'main-tank' via a 2ÁM (97%) to 0,45ÁM 100% filter .... all before it went into the 'main tank'.
Water in the 'de islands' either comes from RO (best and 'usually' safe) or cisterns of collected rain water (worst) ... the cisterns are usually 'open to the atmosphere' (and sometimes stupid 'cruisers' sneak in to these cisterns 'to soak and relax'). In Central and South America, Mexico, etc. the water from remote places can be downright dangerous --- flukes, oocysts, parasites, bacteria, etc. etc. etc.; and, these should NEVER get into your tankage where they can multiply. The low life expectancy in the 'third world' is because of 'bad and contaminated water'.
Simple measures for healthy water on a boat: Filter the water BEFORE it gets into a CLEAN and sanitized tank. If the water tastes like sh!t coming from the tank and tubing, it means there is sh!t IN the tank. ALL components of the tank and delivery system MUST be certified to NSF or FDA for use in 'potable water' to prevent drinking harmful 'leachables'.
Oh yes, consider to put a filter on the tank's VENT to prevent aspiration of airborne FUNGUS, MILDEW, etc. from getting into the tank. The simplest means is to take a fist sized wad of 'bandage cotton', cover it with bandage gauze, keep it DRY and change once yearly; OR, install a hydrophobic PTFE 0,2ÁM(100%) capsule type filter ... about $90.00 from a source that supplies to the bio-pharm industry.
"Will that help keep everything clean? The 3M unit I purchased does filter down to .5 aswell... I'll install it after the pump
just for my own piece of mind."
Absolutely not.... a 0.5ÁM filter without 'certs' of removal efficiency most probably will be a 5.0+ÁM on an absolute or 99+% removal basis.
To keep a system 'clean' .... You have to get inside a water system every now and then mechanically scrub the built up bacterial colonies, etc. off the walls, followed by shock sanitization with clorox, etc. followed by regular and proper chlorination levels to keep the micro-biology from growing.