Dont....
DONT put a filter ON your boat, either a particulate filter, a carbon filter or combination. A filter will accumulate and concentrate bacteria and microorganism and when these ultimately die will dissolve back into the water ... and cause fever, and other 'metabolite' problems including the stinky funk. Carbon will greatly acclerate the growth of microorganisms (its a nutrient source) PLUS it will *remove* any chlorine that the water company put in or that you added to the tank resulting in *faster* growth.If you need to filter the water, filter it with portable filters on the HOSE that you fill the boat with. For carbon the SLOWER you filter the better the adsorbtion - follow the filter manufacturers recommended flow rate' then either halve it or 'quarter it'. When done filtering, shake all the water from the filters and store them DRY. If the tank water is still funky, then its time to get inside the tank and piping and SCRUB out the bacterial scums with detergent and water. Once the tank is scrubbed, then be SURE to change the vent line and cover the open end with a filter .... or a fist sized wad of bandage cotton protected with bandage gauze taped across the open end of the vent --- that will stop the mircoorganism and their spores from being sucked into the tank. How much chlorine/chlorox to add to keep the water safe? TOTALLY FORGET RECIPIES, just add enough chlorox to the tank water so that you can with your nose 'barley perceive that there IS chlorine' ... do this most highly sensitive test at an outlet spiggot. Soon, your 'system' will tell you 'how much to add' on a regular basis - no less, and maybe a bit more if you dont use much water. You dont want to store stagnant boat water for a long time, high turnover usage is the key to a good smelling and safe water system. Hope this helps