Broken record - remove the after cooler every few years for cleaning and pressure testing. Much of the AC crud is not on the seawater side.
Not all ACs are compatible with suggested elixirs on the seawater side. As CE states, check with your manufacturer. For us slowpokes, a fouled AC is not normally a big deal. But once into the 60% and above fuel burn and rating curves, getting the AC clean, on both sides, is essential.