In the interests of full disclosure I'm having a strange issue that I'm trying to address. I love the Purple and blue bulb combo and color wise and growth wise, the corals love it too. Im seeing easily verifiable growth that is quite good. For example, visible day to day spreading of coral bases, cut branches healing over and growing in 4-6 days, etc.
Before I started the increased blue regimen, however, I saw a darkening of growth tips. The corals are certainly growing, and doing well but the bright colored growth tips were just vanishing. On some corals, that's a big problem - like the "surf and turf", where the beauty is in the blue tips. After a week plus of the higher blue light schedule, the tips are still trending that way. I'm a bit baffled as to what is missing to cause this to occur. I attempted to increase the intensity a bit by lowering the lights but I haven't seen any changes from that.
I read a while back that the blue tips were a response to high levels of irradiance, especially UV. Since the tip is growing quickly, the coral is low in zooxanthellae at that location and the pigmentation is used to protect and encourage proliferation at the tips.
I've spent a lot of time looking at the Spectrums of blue plus and superblue bulbs and comparing them to the AquaBlue Special bulb. I've looked at the AquaBlue for comparison because that bulb has produced growth tips within a day or two of adding it for me before.
In the blue/violet area, there is a peak around 400nm that is reduced in the blue plus, as well as more output in the ~485nm area. Obviously there is a big green spike and spikes in the yellow, orange and red wavelengths. Since I use the Purple bulbs that supply the reds, oranges, and yellows, the combined spectrum of the blues and purples should be very similar. In fact, when I use the spectrum simulator, other than the UV at 400, the only significant differences are the green spike and a wider red peak.
ABS put out more lumens and look brighter because of the green peak, but supposedly the 550nm light has no effects in corals. The real world and calculated par is almost identical between a combo of 4ABS and 8B+ and 8B+ and 4Fiji Purple. So I'm bait baffled as to what the missing ingredient is. I will start with the UV by swapping out 2 blue bulbs and replacing them with 2 super Actinic. After a week I'll see if there is a change.