I know that it’s actually side effects of the PH, not the PH itself, that causes the gouramis to die. Sorry, I should have been more careful with my words. I also want these guys to breed; no use having an endangered fish if you’re not going to reproduce them, as this site says!
I just tested a couple tanks I set up with the same soil, and it turns out that they also have a huge buffering capacity. Since most plants tend to like an acidic PH, I assumed that it would be acidic over the long run also. With the other tanks it’s fine(and, in one case, good!). You’d think a soil with peat listed as a high main ingredient could be trusted..oh well. I will redo the tank today with only peat + sand in the substrate. FYI, I do a lot of Walstad setups.
Btw, the gourami that died appeared to have silvery patches, kinda like bunches of scales had come off. Kinda looked like he had been in a bad fight.