I've decided to use either onxy or flourite for the 150 i'm about to get. I like the look of the onyx over the flourite but Sea Chem says that the onyx will act as a buffer- hence raising my Ph/Hardness. Does anyone have any light to shed on this, - will I have to settle for the flourite? PS- I wish to add cardnials and rasporas to the tank which like a bit softer water.