I don't necessarily believe you can feed your fish and grow them fast enough to cause detrimental effects. I have heard it many times before. I would point fingers at hormone laced foods fed in ornamental fish farms overseas and in FL.. I have seen Bala Sharks with abnormally large bodies and tiny heads. and I think alot of guppies/tiger barbs/bala sharks die from these hormone enhanced foods and grow-out methods.
Multiple water changes daily would only cause stress if you allow them to.. Make sure you don't have swings in the temperature or pH. If you are doing water changes this frequently, you shouldn't have to worry about water quality varying.
Just because you do water changes dosn't mean you have to clean or touch the biological media, or even put your hand in the tank. So the idea of having the bio-filter catch up for a few days would only apply if you mess with them.
As far as growth, just monitor your nitrates and try to keep them >20.. Base your water changes on how fast your nitrates grow. A consistent schedule is the best, like %50 every other day, clean the bio-media every few weeks.
Raising temperature will increase metabolism and should increase growth.
Having the pH/hardness of the tank simulate the wild habitat of the fish you are trying to grow will help..
Do some research on photo periods and you can find some info on how commercial fish farms use day/night lighting effects to stimulate the fish to grow faster. Again, this is questionably detrimental to the fish.
Feeding them a high quality food, especially in PELLETIZED form is the best. Alot of Vitamins and Nutrients are water soluble (vit-C), and will dissipate into the water within a few seconds of hitting the water in flake form. A high quality mini pellet (hikari micro-wafers, cyclop-eeze granules) swallowed like a pill will be the most effective for growth and nutrition. Perhaps mix in some high protein frozen foods like Mysis Shrimp or Beefheart.
Might look into medicating your fish for internal parasites too.. If they are looking skinny with all that feeding.. I would try internal parasite pellets, as they are effective.. If you fish don't take them right away, starve them a few days and they will pop them like pills (making them more effective just like vitamins).. If not, treat the entire tank with something like PraziPro as a general anti-parasite bath..
Hope that sheds some light bro'zer.
