I wish I knew. I'm seeing some of the best reds I've ever had in a few corals and I'm not sure exactly why. I will relate my current thoughts and results, but I'm not sure how valuable they are.
This is an unkown, either wild or maricultured.
This is a Red Robin
I really think it has a lot to do with coral genetics and how used the animal is to tank parameters, but it seems truly random coral by coral. Adding CaNO3 to get my nitrates measurable increases the color of the top coral but the Red Robin turns more brown red as above. I have a maricultured bluish piece that turns mostly brown if nitrates are elevated but my green pieces seem to love it.
PO4 stability, not a set number but stable, seems to be extremely important as well. This is my 3rd attempt to color SPS and most successful. I keep PO4 stable around .05 (I use PhosphateRx, 3 drops daily)
My KH stays around 6.7. I would rather be too low than too high.
I have stopped fiddling with the lights, I set the LED's on my hybrid fixture and left them alone and I stick with BigE's bulb combination of 2 Blue+ and 2 Coral+.
I use a larger media filter filled with Seachem Matrix to control Nitrates. It took 6 months but now I have trouble maintaining nitrates. I find this much preferable to using carbon dosing and my skimmate doesn't stink up the house anymore. I would rather have less bacteria in the tank, which I think lowers the risk of infection if I do something stupid and stress the acros.
I do feed Reef Roids but not on an exact schedule. Just like Nitrates, Reef Roids seems to benefit some acros while having no appreciable effect on others.
I do not regularly dose Potassium but I have been regularly dosing a small amount of trace elements daily using AF MicroE at 1/4 recommended daily dose (it contains copper, beware). I doubt this is doing anything but it gets me in front of the tank daily.
I do water changes only when things look off and there is no explanation. My best reds were after 3 months of no water changes ... not sure this means anything except that my export methods seem to be working ok at the moment.
It does seem that reds do suffer when PO4 is elevated based on observations from other reefers however there are exceptions. I think reds are tough because they can easily be brownish while other colors tend to mask the browns.
ramble ramble
I have become a huge skeptic of using any product to improve colors. At the moment, if I had to make a short version, my only conclusions are:
1. If NO3 is clear on the salifert test colors will be suffering. Some pink is always better, 2 to 5 seems to work best for my selection of corals except for one maricultured piece.
2. Stable and decently low PO4 has been critical to my success. Not a magic number, but stable. I say decently low even though the first coral pictured had those colors when my PO4 drifted up to .08 and I increased my PhosphateRx drops to 3 daily. For me this points to how the PO4 number is not as critical as how stable it is. When I was using GFO I had all kinds of issues with swinging PO4 and stressing corals. Using daily drops the drift is slow and levels remain fairly steady.
3. I do not like carbon dosing in an acro dominated tank. We all make too many mistakes and added bacteria seems to increase the risk of infection, sort of like being in an enclosed room with a bunch of sick people. I've switched to using a stable media to control nitrates.
Not sure this is helpful but there it is.
