Very low KH and raising it with KH booster

[Hilde]

Those chemicals will raise the GH but will do nothing for the KH. KH is the carbonate hardness and sodium bicarbonate is an easy way to raise that.

Sodium bicarbonate raises the kh and ph. I need the ph to be lower.

 

[Apistomaster]

I would simply try breeding a pair of A. cacatuoides and see if their eggs hatch well. If so then why bother changing anything?
However, I personally would find your water unsuitable for the species i raise and if I were you I would get an RO unit unless your rain water is abundant and easy to collect. I don't have an option to use rain water because it doesn't rain enough and so I use RO water then formulate to meet the needs of my different soft, acids water fish species.
I keep 2-55 gal, FDA food approved barrels as my prepared water reservoirs and I learned long ago that adjusting the water chemistry in situ with the fish present will eventually come back to bite you.

 

[Mike Wise]

... I learned long ago that adjusting the water chemistry in situ with the fish present will eventually come back to bite you.

Amen! 100%