I have read chlorine may be corrosive whereas bromine may be less so, or even not corrosive. (Conflicting info, on that last.) A boat
neighbor uses bromine, and still has to clean out his strainers periodically.
I have read a piece of copper in the strainer will discourage critter growth. Sounds plausible, given copper was a traditional anti-fouling
ingredient. I have a small copper elbow
in our AC intake strainer, but can't tell if it's useful or not. No marine
growth, but that might be coincidental. And it doesn't do anything about the mud or jellyfish (sea nettles).
It is possible to add an easy-flush mechanism to a raw water
intake system. Google
seacock conversion (SSC) and flush adapter for an example of an already-made-up system of fittings that could be useful for the job. OTOH, dock water
pressure may or may not be sufficient to clean out mud, and I know it probably won't clear a sea nettle from the strainer (too gooey)... and you'd probably not want jellyfish being forced through your AC or similar system, anyway.
Our SSCs are immediately after the seacock and before the strainer, so attaching a garden hose is easy and fresh water
through the strainer and follow-on system helps a bit. OTOH, I still have to clean mud -- and the occasional jelly, sometimes -- from the strainer manually.
I have used the flush adapter to clean the system with "product" -- in this case, Rydlyme -- and that's much more effective than plain pressurized fresh water. OTOH, when I did it, I still removed the strainer baskets and cleaned those manually... so not sure whether Rydlyme (or Barnacle Buster, or similar) would have done that or not. And the cost of "product" can mount up a bit... so I haven't used that more often than about once/year.
In my AC system, I used a small electric
transfer pump to fill the AC plumbing
with the stuff... then let it sit... then flushed. Worked like a champ. For the main engines and genset, I did it slightly differently, using a recirculating approach... which also worked like a champ, possibly even better. But even for mains and genny, I removed the strainer baskets and cleaned them separately.
Doesn't hurt to have spare strainer baskets, especially for the AC system in hot climates. That can at least make part of the process faster. Out with the old, in with the new, clean the old one at your leisure.