>>> IVIassacre <IVIassacre@aol.com> 03/07/98 01:02pm >>> In a message dated 98-03-03 20:14:51 EST, you write: << We had the same problem(high pH) with one tank, turns out the gravel = had fine/crushed sea shells in it. One test for that is too take a sample of gravel (not too wet) and add vinegar too it and see if it bubbles. >> >>Would this also work for regular rocks? Only if they contained carbonate (calcium carbonate in sea shells), the = vinegar provides acid which causes the carbonate to be converted into CO2 = and hence the bubbling. Kathy