Very hard water indeed. You could create a unique Hygro-only tank perhaps.
Did you figure out why the KH goes from 17 to 28 degrees? Is someone adding baking soda to your tanks?
I think if your measured values are correct, they are unsuitable for most plants. 17 dKH might work for hardy plants, but almost doubling that... I don't know.
Did you figure out why the KH goes from 17 to 28 degrees? Is someone adding baking soda to your tanks?
I think if your measured values are correct, they are unsuitable for most plants. 17 dKH might work for hardy plants, but almost doubling that... I don't know.