I use them in my apisto panduro tank. I can not speak to their ability to soften/lower ph. They do give the water a nice stain. The fish apparently appreciate the conditions as they've just spawned. As Mog stated, the decaying leaves will harbor colonies of microorganism and bugs that will sustain hungry fry between feedings, it also gives the clean sand bed a very natural look. I only use them in this tank though. I have apisto spawning in another tank with much brighter light and co2.. dont know how much can be said there.. but that's where I'm at anyways.. i honestly wouldn't use them with discus unless you were trying to go 100% biotope. You'll lose sight of some of the more subdued splendor in their coloration. It's a give and take, I'm sacrificing my wants of seeing my fish in all their natural beauty to give them what is said to be the most comfortable habitat to live out existence in a glass box in my dining room..
Sent from my SAMSUNG-SM-G900A using Aquarium Advice mobile app