I just did this, here is what I did...
New dry pukani rock and one tonga branch to hold the roof over a cave-
First I soaked the rocks in RODI for a week, after a few days the TDS went way up probably just the salt, and as it leached everything off. Then changed the RODI, after the end of the week the TDS was low. Water likes to be dirty, pulled all the nutrients out of the rock. Then I placed the rock into my sump for a few weeks for all the good bacteria & bugs to make a new home. Just today I worked the rocks into my display, still stands out being new but not white like the aggregate. The tonga branch help make a great big cave, very happy how that worked.