I have hard water and I wouldn’t say it doesn’t anything dramatic for plant growth. I would first try to keep track of your fertilizing and lighting. maybe write down when and how much on a note pad and note down how the plants are doing. After a few weeks then maybe come back around to the water issue but I think you can probably get where you want with the light and fert adjustments.
you might also do some research on items like a wondershell or crushed coral. I know those are used to help with water that is relatively soft to help add back in some minerals and it might be easier to measure how much you are adding in. I have not personally used these so I can’t say for sure if they are effective or how they are used effectively.