If you're one of those poor souls who don't "believe in" evolution, this won't help. But there are no rules in fishkeeping other than that fish and plants are diverse, and what works for one, water-wise, may not work for another. There are many fish that have adapted to very hard water, and would thrive in your tanks.
pH is easy to read, but deceptive. It tends to be higher if there are a lot of minerals in the water. Tends. Again, that isn't set in stone (accidental pun there).
It's often a matter of looking at where the fish originates, and then at a map. Coastal species tend to need harder water, as limestone and dead coral are common along coasts. Rainforests have very soft water. I live along the Atlantic coast of Canada, and tested a local lake this morning - very soft and acidic. So we're talking tendencies. In coastal Mexico, relatively recently risen out of the sea, the pH is very high and the water very hard.
We want rules or laws. They just don't work here. Your pH will tend to be what comes from the tap, and almond leaves release tannins and will affect pH in poorly buffered water, but are truly useless except in a cosmetic way. They won't change the minerals, and they are what matter to the fish and plants.