I've lately been to a river (Delaware River, Upstate New York) - it's surrounded by a forest and the river's bed is rocky (although there are plenty of plants on the bottom as well). The water is not salty. Fish such as trouts and browns live there. I found nice pieces of wood there. I also found nice pebbles and rocks in the river. I am changing my aquarium setup and will be adding new rocks, wood, and more plants. Now, I know that neons and angelfish like low pH water (around and below 7.0). I have been told that wood brings the pH down - which would be good for the fish I have. And that rocks, instead, bring the pH up - which wouldn't be good at all for my fish. Firstly, if I use rocks, could I use the rocks I found in the Delaware River? Secondly, if these rocks are to bring my pH up, will it be safe to use these rocks together with wood and more plants? Will more plants and wood neutralize the strength of rocks and keep the pH relatively safe for my angelfish and neons? Also, when I am adding a lot of plants, will I need more gravel / substrate? If so, how much more? Is there any special kind of gravel necessary for the plants? Or will plain gravel suffice?