plants seem to do best at 30ppms, I dont think anymore would benefit them. not sure though, don't take my word for it...
In the custom gaming computer world, a situation like this would be deemed "bottlenecking" or being "bottlenecked" lolJust remember that your growth rates will still be limited by the lowest available nutrient. (Lighting, ferts, CO2)
no the drop in ph associated with injecting co2 will not hurt plants or animals what does hurt them (animals) is the lack of o2 that comes with water that is too saturated with co2.Couldn't running your CO2 too high lead to a pH drop that could kill your plants? Assuming you're not buffering your pH with your substrate or crushed coral or something? (Soft water here...)