I have a 110 g tank with an Orbit PC 4x96W light and CO2 injected. Using a pinpoint mon. in the morning the PH is 6.8 and before the lights go out the PH is 7.0, is this good or bad? I have a Red Sea drop checker , is it to small to be accurate? I made my own KH water using API KH test kit , the drop checker is always green, although it is much darker than than the shades given on the color charts for the PH. Should the KH test kit be calibrated. I am using the EI method.