I also have very hard and very alkaline water from the tap and it does give some problems with some plants as many of the shop plants are aimed at the group who have softer water. But that just means I have to sort out which plants and which fish do like hard water. Many will say that you can't grow plants in hard water but that is pretty well ignoring that there are plants in almost all water of all types. Think of the springs in Florida and Texas where the water is coming straight out of limestone?
But for better growth without changing plants, I might look to ferts and CO2. Those are major food groups for plants, so maybe bumping it up is the simple start.
Point to keep in mind is that we kind of use the drop checker as a guide to what we might be getting in the CO2 line as it indicates we are getting enough to drop the PH one full degree. That's based on the idea that 30 PPM is good for CO2 and we will get that much with a full point drop in PH. There are some charts but those charts do some assumptions that may or may not be true, depending on what and how much of each mineral we have in the water. Assumptions, guesses, guides or estimates only? The idea is to give us a starting point and then we may need to adjust from there.
Feeding the N,P,K macros and a bit of micros? If not consider feeding the plants but if that is okay, also look at more CO2 as it should be pretty easy to just turn it up a bit, while watching the fish for a few days as it does reach a stress point at some level. Work it slow, if all is okay, bump it a bit more but watch the fish!
Expect either to get more growth or the fish begin to stress with obvious breathing problems. If neither of those try boosting the ferts. Farming is not a simple thing, but more a matter of simple observation and adapting to what we see.