I'm guessing that they add those substances to increase overall hardness, to counter any potential water softening effect that the almond leaf extract may have. Can you buy, or pick up Catappa leaves locally, and make your own extract?
Thx for input. Yes I can get Catappa leaves from Chatuchak market pretty easy -- but in fact your guess is actually what I'm hoping is true: while I want at least some of the benefits of almond leaves/tannins I don't really want to bring down PH (even though in their natural habitat it's lower), as I think too hard to sustain it. I know 7.9 PH isn't the best for Arowana long-term development but I'm thinking stable is better than fluctuating. Also I'd bet they've grown up 99% of their lives in regular tank water, not pond or black water.
In any case from the smaller sample test I did yesterday the PH actually didn't seem to change at all after adding the 'Spa' solution (but as I was advised on another thread this may also be partially due to the fact my KH/buffering is reasonably high at about 7).
That said I think what you said is true -- also it's made by a Thai company and most places here have pretty high PH, which of course they'd have to be aware of.