I think the biggest problem with damaged hair is that its more porous, and so soap scum builds up in all the little nooks and crannies, and an acidic rinse doesn't do much. I have found that adding a squirt of conditioner that contains disodium EDTA to my acidic rinse helps with the buildup a lot. EDTA is a chelating agent, as are citric acid and ascorbic acid.
Because of this I'm thinking of trying to make a rinse containing all of the above three, to experiment and see the results.
I ordered EDTA and L-ascorbic acid today, and I will be trying different recipes. I found a post about "Miracle Water" a few days ago, where you add about a quarter teaspoon of citric acid and a pinch of ascorbic acid to a quart of water, and use only this on your hair in the shower.
I was thinking of bringing this up a notch and also adding a pinch of EDTA to this, and hopefully this combination would help remove most metal ions in the water.
Of course this is irrelevant if your water is soft.
Ill post my results when I receive my order. Can't wait! I love experimenting