Purple up won’t work. It doesn’t contain coralline spores. Just the extra nutrients they need to grow, most of which are doses as part of keeping corals anyway.
ARC coralline contains spores. It legitimately works. Could you get a couple dead snails and scrape some off for free? Sure. Could you scrape up enough to get full coverage of 100lb rock in 4 months? Doubtful. There’s a local guy that went from brs reef saver to complete purple and red coralline in 4 months. Added it the day after he confirmed his cycle was done. And the reviews on amazon support this guys experience
I’ll be adding a bottle of each of the red and purple sometime in February, once I’ve got my levels stabilized and my current QT residents in the tank . I plan to do a full review, with pictures