OK, so listen very carefully, because what's happening is that you are discarding bits and pieces of information and choosing what things to absorb. This gives you an incomplete picture and severely hampers troubleshooting.
We do not care about what the parameters were "the last time you tested", because that tells us absolutely nothing. What we're requesting is for you to to take pH readings over the course of the photoperiod and report all the values from sunrise to sunset. So if your photoperiod is 8 hours long then we need to get at least 8 evenly spaced pH readings. 16 evenly spaced pH readings would be even better, but 8 will be sufficient. This data will tell us just exactly how effective your CO2 technique is because CO2 drives the pH in the tank.
The DC is also a pH test kit and so it's colors should vaguely reflect the pH trend in the tank that you will measure.
It could easily be that although you think that you have a lot of CO2, you might actually not have a lot. That's what we need to find out, and the only way to find out is to take multiple, "time-lapse" pH readings in the tank.
Forget about everything else. Leave the tubes, diffusers and everything else where they are as shown on your page 1 sketch and take the measurements. Then, we will make a change to something and subsequently, take the measurements again to see if the change that was made was effective. You have to be systematic and methodical, because CO2 is very complicated, and we are all separated by hundreds or even thousands of miles, so we cannot see things clearly enough to solve the problem. These measurements give us the information we need to suggest a course of action, but only if we are disciplined enough to make small changes from a known configuration - and so we have to know exactly what the configuration looks like, otherwise it becomes a lottery, get it?
Cheers,