We just purchased a used 180g Acrylic tank ... use good old generic potting soil topped with gravel... but I want to consider all my options.
I believe I read a ph of 6.8 is optimal for Discus. I really need to check the ph of my current tank to see where it is at and if it has a good ph for discus.
I would suggest doing more research into keeping Discus, especially if you are not going to buy adult size individuals. It's best for you and the fish to be focused and not force two things together unless you have loads of experience in both things. The pH of the tank will be your last problem in a tank with potting soil/aquasoil as substrate and juvenile discus. Captive bred discus are able to live in harder water and higher pH than the wild individuals. They still need lots of food and clean water, however. A good starting point is here : SimplyDiscus
also float your ideas by @discuspaul
, he knows a thing or two about discus
For what it's worth, potting soil will also release a good load of NH4 and will lower the KH and pH if enough humic (and other) acids are there. Here again the problem of consistency and confidence into what is going to happen.