You rarely get to build a new neighbourhood here, often it's renovation work done on already built areas. Building a whole new block all the time is simply unsustainable.
I think the diffusion rate of Ca and CO2 is also important. Even though the ocean is supersaturated *globally*, the local area around your plant might not have enough concentration. Hope you can get someone to check that.
Might have to spread your plants across multiple regions, or place it around somewhere with low impact to marine life I think.