Jerry Vinegar is an acid.... you test it on rocks to see if they have calcium or limestone in it... if it bubbles... this tests positive for those things, which will raise your pH and make your water harder if you use those rocks.... rocks like Quartz, garnate ...... igneous type rocks dont effect pH... Thats the extent of my chemistry lesson.... Im sure someone will come here and explain it better , give you more scientific responses.... but thats the just of it.... if it dont bubble when you add vinegar , it wont raise your pH... safe for apistos.... sort of John Now remember your old high school chemistry teachers saying..... little Johnny was a chemist, but Johnny is no more..... for what he thought was H20 was H2S04. (Sulfuric acid) ------------------------------------------------------------------------- This is the apistogramma mailing list, apisto@listbox.com. For instructions on how to subscribe or unsubscribe or get help, email apisto-request@listbox.com. apisto-digest@listbox.com also available. Web archives at http://lists.thekrib.com/apisto Trading at http://blox.dropship.org/mailman/listinfo/apisto_trader