Purple up to me smells like money going up in smoke. NO need for it ever and my coraline grows just fine.. Proper water changes, SG, temps and light, maintain calcium and alk levels along with all other proper water parameters and coraline will grow just fine. I jump start my coraline growth by usuing a nice heavily covered rock with coraline,and during cycling I keep my alk and cal and ph levels as High as possible without the calcium precipitating out. I can normally initiate coraline growth within the first 30 days of a tank being setup. After tank cycles I do a water change to get levels back down to reasonable levels, or just let it go for a bit more time till higher levels are utilized. Normally high calcium does not hurt anything.