From Tom Barr's research with his CO2 gas reading equipment I would say no.
He found up to 100ppm close to the source of CO2 (diffuser) and as low as 10ppm further away.
If too high CO2 were a problem then I assume the plants closest to the diffuser would struggle which as far as our tanks show is not right.
We stick our DCs in the furthest corner so this means that green on the DC would be yellow closest to source. A yellow DC further away would mean ? closer to source which is of course as far as the colour will go due to the Ph tests limit.
This is also one reason why we put the DC closer to the surface in the opposite end to the source. If it were near the substrate and we aimed for green the likelihood would be that the further up the tank we went would be incredibly high and at source deadly.
We are not aiming at 30ppm all through the tank. We are aiming at ' a good level' around the tank and therefore the 30ppm is an 'average' which means a certain level is available in the poorer parts of the tank (namely substrate area) and then high levels are available at the source.
This is also one reason why Ceg and I (and an increasing amount of others on barrreport) are now thinking it isn't highlight but high CO2 that is the determining factor with some plants. Meaning under what is asumed to be 'low light' if we crank the levels up slightly and/or improve circulation drastically then the 'high light' plants suddenly start to 'work'. People forget that they also 'improve' CO2 the more light they add
AC