I have been trying to fight off a light hair and brown brush algae problem. Most things I have read mention low Co2 can contibute. I inject Co2 controlled by a Pinpoint Ph meter which reads a Ph of 6.7. It is a 54 gallon and based on the Ph/KH chart I should have plenty of Co2. But to make sure I obtained a drop checker and 4dkh standard. I ordered an API ph kit for the indicator. After receiving the kit, just for couriosity, I checked the Ph with it. fully expecting it to be in the ballpark of the meter. However it is way off. it is reading about 7.2 while the meter reads 6.76. I then checked the tap water, meter reads 7.14 and kit reads 7.4-7.6. I calibrate the probe regularly and it always calibrates well. I noticed my drop checker with 4 drops of bromethly blue from the kit and the standard is still blue after 3 hours. What could be wrong? Is the API kit way off or is my tanks ph being lowered by drift wood, aged substrae (about 8 years old now) etc. If it is being lowered by other things in addition to Co2, if I add Co2 till my drop checker turns green it would probably lower the ph to 6.0-6.2 or so. That would be way to low. What should I do?