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.

the red sea checkers are fine, remember the less volumn of solution the faster theyll react, the red sea checkers are actually really good because they minimise the amounts of solutions needed to get a good clear reading. the light/darkness of the colours is generally only down to how many drops of reagent you use, the more - the darker.. it wont effect the result, just make it a bit harder to read it under some conditions.

you might find that not much co2 is dropping out over night through lack of surface movement, it makes a big difference.