First, leave fresh water for a later discussion. If any of you have ever tried to operate a salt water aquarium, you realize just how precarious the balance is. You lose O2 and you lose a lot of $$$$ fishes and marine life. My sea water system-- up until today-- consisted of 3 x 1 1/2" bronze, clam shell, TH's, each going through a big Perko strainer. One for each main and one for the sea chest which supplies water for the genset, AC sea water pumps and the RO water maker. Calculations say this is more than sufficient flow. When clean. A little growth and the flow decreases. Genset has an impeller and so takes what it needs, leaving AC and RO centrifugal pumps with whatever's left over. With a semi clean intake, I can run the genset and AC. Or RO but not both unless I've just cleaned the clam shell. Now. . . I've noticed I rarely have to clean the main engine strainers; they produce little if any growth. Why? They are poor salt water aquariums. Shut down the mains and in 30 minutes or so, life ceases. O2 is consumed by O2 organisms and they die. CO2 needers die too coz there's no longer any plants to produce CO2. Dead, smelly water. For the purposes of engines, it's clean water. Engines running, you'll see a little growth but not much. Been running down from New Orleans the last several months and it is not a problem. The sea chest is. Now, the sea chest is a horse of a different color. If I just ran the generator a few hours a day and shut it down, it would revert to the main engine paradigm of dead water/clean strainers. Plugged into shore power, I build the perfect salt water aquarium. Nutrient, O2 suffused water continually flows through my strainer by the AC cooling pump and stuff grows. Really grows. Slime, barnacles, little shrimp and crabs, you name it. That's what we're talking about with strainer baskets. Having smoked one too many generator sea water impellers whilst cleaning baskets, I decided to separate the AC and RO sea water intakes from the generator cooling water. To that end, I constructed a manifold with an isolation valve in the middle of sched 80 PVC. Front half gets clam shell water and goes to genset alone. Well it does have a couple valved hose barbs to feed a main in a pinch. Aft of the valve goes--will in a coupla days-- to a second 1 1/2 TH and strainer. From it, I'm plumbed to the AC sea water pump and RO inlet. All strainers and piping are below the WL. The new TH is a straight, 1 1/2" bronze, mushroom with a ball valve on it and a T instead of an elbow. Gets marine growth, I turn off valve and remove the T pipe plug. Open valve and run a broom handle down into the gulf. No growth, barnacles or plastic bags remain. The entire run from this TH to the strainer in the ER has cleanouts. Hit it with the same broom handle or pressure washer. Makes for a far more easily managed salt water aquarium. Run my bow on a Mississippi mud bank and block the clam shells? El no sweat-o. Close those TH valves and open the manifold isolation valve and all machinery is sucking water from the TH which is back by the wheels in presumably clean water. My 2 cents. Still don't know about chlorine tablets or pieces of copper in the baskets. Regards, Larry M/V Cigano, Prairie 47 Currently lying: Key West Harbor