Thanks for the favorable comments…They are appreciated…

As far as back flushing with fresh water is concerned…I can’t say much about marine growth in your area…
But if you were speaking about this local…I’d say pretty much all they are doing is wasting fresh water…

Shutting a system off for a few days will starve the organisms of oxygen and stop/slow growth…(It’s why they don’t show up in engine cooling systems, or seawater supplied heads)
But some folks are either not willing, or can’t to do that…They want it cool when they arrive…Or they have water cooled refrigeration tied into the pump as well…
A running system however will not allow growth in the condenser coil itself…It’s too hot in that section of the flow path…
That’s not to say though, That the condenser will not accumulate hard water scale acting as an insulating blanket preventing efficient heat transfer (like a dirty radiator in your car)

Down here we tie growth to pump flow & run time…The two seem to coincide…
The slower the flow it seems…Allows them to attach easier. (Faster boats underway most of the time seem to get less bottom growth too)
The longer the pump runs…Just gives them a more constant flow of oxygen, and the fresh food to get bigger.

The newer digital controls seem to have helped for single A/C system boats because the pump only runs with the compressor when the T-Stat is calling for cooling…Thus less pump run time.
Older 3 knob controls ran the pump on the fan circuit and thus anytime the fan was running…So was the pump…You can change this by wiring the pump to the compressor circuit (after the T-Stat)
However on boats with multiple systems on one pump…
The pump runs pretty much all the time because one or the other of the units is likely calling at any given time (If they leave more than one system running, or have water cooled refrigeration)

Some folks say when I tell them all this…OK…I’ll just run One system while I’m away…Thing about that is…One system may not be enough to satisfy the T-Stat in the summer, and thus more pump run time…

My Opinion ?…Best thing to do is either shut everything off while gone…Or to setup & utilize the Humidity program of today’s digital controls to reduce run time while away….

We do have customers adding Bromine tablets to the sea strainer basket with some success and there is also a product out called Bio-Guard that is nothing more than a copper tube inside of a PVC sleeve…
As the copper deteriorates it releases into the water stream copper oxide (active ingredient in most bottom paints)
I have installed a few…End of summer should let us know how they work.
You could also try pieces of copper tubing cut to fit into the strainer basket…I’m getting pretty good reports on that.

Again Thanks for Your Interest…I hope I helped some…
Steve~