I don't believe you can honestly say "without a doubt". There's plenty of threads debating this, so I won't get into it too much. But you did not do a blind study, no structured experiment. You used it and had good coralline growth. I did not use it and got good growth. Whose to say it is the cause of yours? If they marketed it as a supplement for Mg and other trace elements (that you do not need) then fine. But by naming it Purple Up they are implying it helps Coralline growth. Coralline requires stable parameters at high yields. You can not maintain that with purple up. It's snake oil. If I gave some kid a pill that said it would make him grow faster... well, who could prove it did or didn't. Each tank is different. Coralline grows, it just does. Kids grow. You can't objectionably prove it works but you can prove you don't need it. Buy it if you want, I don't think it'll hurt too much. Throw your params out of whack for a bit... I don't think you should be sticking up for the one doing the misleading... I'm more concerned with fair to the consumer.