[Bill Little]

Let me take a stab at this issue… I am not too worried about the pH but the measurement I follow is conductivity or TDS depending on what meter you have available. If you are utilizing RO water the conductivity should be well under 50 mS which is where you want the water to be with Paros. With low mS you normally have a low pH. I believe what Helene is attempting to say is with adding additional amounts of tap water, even in small quantities, you are re-introducing trace element i.e. NACL and other minerals which will in itself raise the pH. The more tap water you introduce,the more mineral content you are adding back into the tank, the higher the increase in pH, the higher the conductivity or TDS. As the pH increases you will attempt to lower the acidity in so doing you will have a tank that will become unstable.