Yeah Orient, you are right in the sense the coral will harden up the water but I think the driftwood is leaching alot of black water as well which will soften the water. As long as the water hardness is being monitored, I think using the coral is much better using those "pH up" as the product is expensive and alot is needed to condition the tank as the wood is leaching the tanin and acid continuously. Maybe there is a cheaper alternative to bring the pH up ... which I dunno of.