Welcome to the forum!
I also live and California and am also suffering from hard water. California usually got it’s water from the Colorado river, but since the river is extremely low right now, California recently switched to getting its water from an aquifer! So the water used to be good as is but it’s now extremely hard. What worked best for me due to limits in pricing and needing a fast softener was api water softening pillows! It’s fast but slow enough that it doesn’t hurt the fish and you don’t need to worry about the chemicals. You need one pillow for twenty gallons of the tank and all you do is stick them right in the filter. So your tank would need 2. The pillows need to be recharged in an aquarium salt bath every couple days but they really work and my soft water fish are looking much better. Took me a couple weeks to get my water params in a good spot and now I only stick them back in the filter when I do water changes.
If you have the money, an RO system would be best to get your water to the correct params but it’s expensive, slow, and wasteful. But it IS the best for the health of your fish. A solar still is a free alternative that produces no waste, but it’s extremely slow.
