I also use a small amount of aquarium salt to further soften the water.
Aquarium salt (sodium chloride, sea salt) will not soften water, nor do anything else for that matter. But this common salt will harm all freshwater fish over time, so discontinue using it. Salt is useful as a treatment for certain issues, depending upon the fish, but has no benefit long-term and as I say is very harmful to freshwater fish.
I use Indian almond leaves and have a water softener pouch from API that I have ready to use if it becomes a problem.
Indian almond leaves will have little if any effect softening water when the GH is high. The GH and KH (Alkaliinity) of your source water will not be likely to lower unless you dilute the water with "pure" water. Pure water is distilled water, reverse osmosis water, or sometimes rainwater. This is a complicated business, but I wanted to mention that the high GH is going to resist softening agents.
The API softener I am not aware of, so I cannot comment on its effectiveness. I would question if it actually lowers the GH/KH though, as there are hundreds of aquarists with hard water that would welcome such a tool and I've not heard of this previously that I can recall.
The pH is related to the GH and KH, but not an indicator of those values. It is the GH that is most important to fish, be they hard water species needing this mineral in the water, or soft water species requiring softer water to whatever degrtee depending upon the numbers and the species.
The Pentazona Barb,
Desmopuntius pentazona, is a less active barb but one requiring fairly soft and acidic water. More info here:
http://www.seriouslyfish.com/species/desmopuntius-pentazona/
