You can add a drop of API pH indicator to both solutions in the double bulb drop checker and get a more intense, easier to read color. I verified with Cal Aqua that this will work, and tried it myself successfully.
If you stop looking at pH, and start working to get good CO2 concentration and distribution in your tank you will gain a lot. It is going to be hard to get good distribution of CO2 in that big and long a tank without using at least two different injection points in the tank, and really good water circulation in the tank. A Koralia type powerhead or two would help a lot with that.