| Purple up is an option, not a necessity. The availability of calcium and calcium carbonate in the tank are going to have the largest effect on the growth of coralline IME. Some salt mixes have varying degrees of these nutrients in them and will serve to set a basis in the tank. Test the calcium level of the tank and use either Kalkwasser (recommended), Purple Up, or any of the other available calicum supplements on the market (I use Kent Tech CB and C-Balance as well as Purple Up) to maintain the level between 380 -450 ppm. I have noticed that the closer to 450 ppm that I keep my calcium at, the more growth I get from the coralline.
As far as color goes I don't believe anyone truely knows what influences the color this algae takes on. It is found in pink, purple, red, maroon, yellow, green, and others and oftentimes all of the above in the same tank. Lighting spectrum and intensity do not seem to have any effect so far as I have seen and read.
Purple is the predominate color of coralline though, and so long as it is growing in your tank you are bound to get the purple back in great quantity.
HTH,
Aaron
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"The only thing that happens fast in saltwater tanks is failure."
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