Hi Arkangel77,
Been reading your thread, and it kills me that you're going through some of these fustrations with your beautiful tank and Discus fish.
Debbi and Connie is pretty much on the ball as to helping you with your troubles.
A few things that I noticed you mentioned, RO water, plants, additives, and white poo. I'd like to address these and talk a little more about these.
I noticed that you have different aged Discus in the same tank, generally they should be kept seperate due to their water requirements. Younger Discus tend to like harder, higher TDS water and make more of a mess and require higher temps to grow out to their full potential. This is where you hear the 88 degree, 80% water change a day, barebottom, tap water, and higher GH comes to mind.
Adult Discus does not need the higher GH and TDS, and would prefer a lower TDS when it comes to breeding. They no longer need the higher temps, as they are fully grown, and don't need the extra temps for metabolism. They can do well from 82-86. This is where you'll hear about 50% water changes a week, lower temps, RO Water, RO Right, Black Water Extract, Almond leaves, PH 6.0-, etc.
I believe that RO Right and Discus Essentials is a similar product, both will add minerals back into the water. I would choose one, or the other, but not both. These products are aimed to increase the GH, KH, and TDS of the water. It's important to keep these parameters stable, which brings me to remind you that weening them from RO Water all in one shot is not advised, slowly bring in the 100% tap water if you wish to do so through small water changes.
White poo, as pinkertd have stated, it could very well be the stomache lining, but it could also be internal protozoa. Metro would be the advised course of medication if this does not go away, and the fish continues to refuse food. I could give you more symptoms of a hex infestation, but we'll cross that bridge when we get there, just have this med on hand, as it usually comes hand in hand with Discus keeping.
I hope my little bit of info could help a little bit in understanding what these fish prefers, and what's practiced by some of the more veteran Discus care givers. I myself has one through a series of what you've gone through, and I'm still in for the long run. You can check out my thread if you haven't already, just search for Ongoing Battle with rescued Discus.
Good luck, you're in good hands.
Shawn
