Las
How did your LFS test your po4?? Just questioning the legitimacy of the original test. If the LFS test was incorrect, then adding 3X the GFO and 3X the GAC may have stripped vital nutrients necessary for the corals health (resulting in common stress reactions like bleaching and tissue recession). Sometimes systems with delicate SPS, the GFO can be too agressive and strip nutrients too much resulting in stress and illness. I've not heard that occur as commonly to LPS (I believe they are more adaptable to changing nutrient levels), but as I said before, often LPS come from waters which are more nutrient rich possibly making them sensitive to very quick drops in nutrient levels.
In regards to the salt mix, I believe your observation of seeing loss of coral coloration and seemingly stressed reactions says enough to indicate your tank isn't reacting well to the mix. It is possible that the organics in the mix are facilitating biological processes to lower total DOC's and POM in the water thus making your water far more clear and making the light far more intense than your corals had been used to. Certainly a possibility and if that truly is the problem then your corals will react positively by raising the light and they will likely eventually adapt to the change in light and resume a more natural coloration. I would assume that after several months the corals would have adapted by now (if increased light penetration is the problem).
Personally, I think it sounds like your tank is reacting to a very quick drop in nutrients. The bioactif salt could have been very slowly removing necessary nutrients (dissolved organics), thus the slow change to pale coloration and signs of stress. Adding the large amount of GFO and GAC simply added to the problem already at hand. Just my opinion.
Pale coloration is commonly a sign of corals being in too intense of light (or not properly photoadapted) "or" being in conditions which are very nutrient poor (too limited in nutrients for the corals proper health and coloration).
If I were in your situation I wouldn't be too quick to change your salt mix to something completely different. To find the most appropriate salt mix I try to choose a mix that already matches the tanks water parameters your maintaining. For example: If your alk has been steady at 8.0 dkh then I wouldn't suddenly switch to Reef Crystals becuase the alk commonly tests out at 13+ dkh. You can find a whole list of salt mixes and their common ca, mag, and alk levels in the first page of this thread.
http://reefcentral.com/forums/showthread.php?t=1287118
By choosing a salt mix that already matches your waters target parameters you will limit any stress from elemental fluctutations from your water changes (I personally believe alk is BY FAR more important to match than ca or mag). If you agree with my theory that your corals are reacting to low nutrient conditions, then continuing to use bioactif salt would be contraindicated as it seems to promote bacterial prolifertation which assists in lowering DOC's (again, that's just a theory based on a common observation from people using the salt).
I would go back to using your normal amount of carbon which will absorb any toxins released by any stressed or dying corals. I'd remove the GFO entirely and continue to monitor po4 levels. If po4 increases then add GFO slowly (starting with maybe half the recommended dose). I wouldn't add any large amounts of AA's. Small doses may be OK but don't dose too much. Nothing is good in high amounts in a reef tank. A gentle and delicate equilibrium of various processes (filtration, supplemention, light pattern and intensity, etc...) is what makes most tanks successful and the concentrated supplements available to us can turn equilibrium upside down and cause a domino effect of problems. Small amounts of AA's may help replenish "some" vital nutrients, however the corals need much more than AA's to maintain normal health. All of the vital nutrients and most trace elements can be restored by feeding more high quality fish food to your fish or providing a variety of zooplankton for the corals.
I agree entirely that all changes should be done very slowly - including changing feeding routines. Eric Borneman has a great series of articles that provide a good explanation of how a tank has a mini cycle with each chage we make. Any little change we make requires the tank and it's inhabitants to change and adapt in one way or another (sometimes a change we are aiming for and sometimes not).
http://www.reefkeeping.com/issues/2002-07/eb/index.php
Jeremy
