The ongoing debate about chlorine tablets is interesting. But, for those of us who shut our A/C systems down periodically, we have what we think is a better and very easy solution. Years ago, we drilled a hole in the top of our A/C seawater strainer and tapped it for a 1/2 inch ball valve. On the other end of the ball valve we installed a garden hose click-on-click-off fitting. After we shut down the A/C we hook a fresh water hose to the strainer and turn on the ball valve. After a minute we turn off the seacock. Fresh water now circulates through the entire A/C system. After a few more minutes of running we shut it down. Now the A/C is full of fresh water, which does not support barnies and most other marine growth. This set-up also makes it dirt simple to flush the entire A/C system with detergent or acid, on those rare occasions that it needs it. We hook a hose to the ball valve and open it. The other end of the hose goes into a bucket full of whatever chemical we want to put through the system. We remove the discharge hose from the A/C discharge through hull and re-route it to the bucket. Now, we go the relay box for the A/C units and put a jumper on the pump relay. Presto, the contents of the bucket are circulated through the system until the jumper is removed. Some day I'll put on a switch to do this on the relay box, but the jumper is so easy that I'm not very motivated. We installed a 3-way valve in the discharge line but have never installed the extra hose to use it...it is simpler to just disconnect the discharge hose and run it to the bucket...maybe some day I'll add the extra bit of hose (sigh). Maurice & Louise-Ann Nunas M/Y AKAMA, KK48 Whaleback (Currently in New Zealand)