I just saw this article that Denver Water is going to be raising the pH in the municipal system to between 8.5 and 9.2! I am already struggling with high pH and I really don't can afford an RO system at this time.
Denver-based here too. It says that they will be raising the pH using sodium hydroxide. We will have to see how that impacts the levels of sodium in the system. If it starts to build up, it could create a lockout situation for the plants. However, small amount of sodium can be good for plants.
To keep the pH lower, you can use phosphoric or muriatic acid. Or, increase your feeding rates and the nitrification process will bring the pH down too.
If this water change proves to be problematic, we may need to start using RO filters if basic sediment/carbon filters can't pull out the sodium.