Jim, the effects of chlorine on a sound tank
aren't immediate, they're cumulative. Just carrying chlorinated water for years does FAR more damage than just an annual or semi-annual "shock treatment...adding bleach to each fill contributes to the problem. If your friend did that, I'd say, yes...that did contribute to his problem. It was also a waste of bleach...because you can't add enough, and still be able to use the water, to accomplish anything. The same is true of H2O2...an ounce or two in 50 gallons of water isn't even enough for the "critters" to notice, much less surrendur and die.However, an annual recommissioning according the directions in the "Fresh Water Maintenance" article in the HM forum reference library--which does call for bleach--won't harm the system, and SHOULD eliminate the need to add ANYthing to the tank with each fill.You've obviously bought an older boat (without a pre-purchase survey, I'll bet) and now you're finding out all its problems--corroded tanks and even corroded hose clamps. That's what neglect does. I also suspect your "fun" is only just beginning. You can bite the bullet and make all the repairs according to ABYC standards...or you can apply whatever "band-aids" are easiet. The first approach will give you years without problems...the second is a crap shoot.