On numerous posts, I have recommended World Organic liquid multiple B vitamins in raisin concentrate for normal molting and to prevent and treat abnormal soft molt. I get these from my local health food store, Natural of Course. You can also substitute human multiple B vitamins tablets, just make the water canary yellow.
In addition to B vitamins, make sure your birds are getting amino acids especially methionine. I use a vitamin amino acid supplement called Miracle from Italy which I get from ABBA Products (they call it AA Miracle, don't forget the AA or the clerk may not find it in their computer).
I also recently tried the Biodecken brand, Molt and Optimix. adding the B vitamins to these products resulting in observable tightening of the flanks. Even though it is only mid August, my birds look so good you would think it is mid October. I purchase Biodecken products from Ricardo Sanchez, 214 998-7474. (In addition, I use Biodecken novafood nestling food, neonate formula and their multiple vitamin and immune support.)
Optimix Metabolism Ingredients: Chelated Selenium, Chelated Chromium, Chelated Zinc, Chelated Copper, Chelated Iron, Chelated Manganese, Chelated Cobalt, Chelated Magnesium, Calcium Gluconate, Potassium Iodide, Calcium saccharate, Surose, and Glycerin.