Boiling water will reduce the temporary hardness (KH) but will not effect the general hardness (GH) to any extent. Therefore, the temporary hardness will increase naturally if the aquarium contains rocks or gravels rich in calcium. Matt Clarke M.Sc & DIC Course in Advanced Methods in Taxonomy and Biodiversity The Natural History Museum, and Imperial College, London. NHM Tel. 0171 938 9241 Home Tel. 0171 635 0618 E-mail:m.clarke@nhm.ac.uk You can view my CV at: http://allserv.rug.ac.be/~booghe/eas/job/indexr.htm ><> ><> ><> ><> ><> ><> ><> ><> ><>><> ><> ><> ><> ><> ><> ><> ><> ><>><> ><> ><> ><> ------------------------------------------------------------------------- This is the apistogramma mailing list, apisto@majordomo.pobox.com. For instructions on how to subscribe or unsubscribe or get help, email apisto-request@majordomo.pobox.com. Search http://altavista.digital.com for "Apistogramma Mailing List Archives"!