While we are on the subject of PH, I wanted to pass on something I have figured out. I have two tanks in which the PH tends to drift upwards. I set up a third tank in my son's school and when I put in the substrate, I saw that it was filled with little bits of sea shell. I went back and took a close look at the substrate in my two tanks at home and saw that tiny bits of shell were mixed in. The stuff I was using was made by a company called Estee and the product is called "natural aggregates." The problem seems to be in the darker gravel. Most aquarium stores in the New York area stock only Estee gravel. Needless to say the bags that the stuff comes in assure the buyer that the stuff is completely inert. I called the company and was told that while no sea shells are supposed to be in the gravel, if someone forgot to clean the machine, then who knows. Needless to say, this did not reassure me. I don't know if this product is local only (the company is in New Jersey) or if its distribution is broader, but I urge caution. M. Diller ------------------------------------------------------------------------- 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.