Thanks guys! I ordered the soil and decided to give it a whirl. The tank I'll be converting to dirt is already stocked :/ but I think it'll be ok. I'll move the fish and half the tank water to a holding container and then drain, dirt, sand, fill, and do a few water changes until the brown and yellow goes away lol.
I've got a lot of extra osmocote plus tabs though. I'm guessing I don't need to use them in a dirt tank? I'll still use liquid stuff like potassium and iron. My java ferns just do so much better with it! Would using tabs as well be redundant, harmful, or add an extra kick?