Purple up doesn't work. Coraline requires calcium, alkalinity and especially magnesium to be at correct levels. Magnesium gives it its color. It also needs some live rock with coraline, a snail with coraline on its shell, or something else like that to seed the system. If you don't have that you will never get it. You can buy two part, pretty cheap I use the BRS two part kit, it consists of additives for calcium, alk, and magnesium. You also would need test kits for all three. One rule is never add any supplements if you can't test for them. You can also use some thing like a razor blade to scrape the coraline you have on something else to help spread it around your tank. It can take a while for it to take hold, several months for me. It first tends to start on plastic, so power heads, filter returns, etc. Another factor is nitrates and phosphates. If they are too high it doesn't really grow and what you do get is green. I moved my system to a new tank in early March. My rocks have a decent amount of coraline but it is just now starting to show up on the new plastic, tiny little specs on my overflows.