My source water is luckily that high, but you can add something like crushed coral in a media bag to your filter. It will buffer the hardness and raise the pH. It erodes over time, so will need to be monitored and replaced. I think as long as you add it gradually, all of your fish will likely adjust. Really as long as your pH is over 7, supplementing diet and adding things like wondershells (or vacation feeders out of the flow of the tank) will help as well. Another option is to dose Kents Liquid Calcium (for marine tanks) diluted to the water column as well. Some contest that this works, but many snailers say that it has amazing results. I typically take a tbsp or so and dilute it in tank water and add a small amount a couple of times a week, being careful to not pour it directly onto tank inhabitants.