Join Date: Jul 2010
Location: Outside Philadelphia, PA
Adding minerals back to RO water is rather easy. There are many commercial products available to adjust GH, both dry and liquid. You can use baking soda to adjust KH. A couple of test kits and your all set.
You can also a mix of tap water and RO water. For example, your tap water is 40 ppm, lets say you want the water to be 10 ppm. Use a mix of 1/4 tap water and 3/4 ro water.
BTW, I use RO water as a base in my planted tank. I was sort of lucky because I already had the RO unit because I also have a reef tank. I found that using the RO water and building it back up gave me better results. I think this was because the salts used were in better proportion to what was coming out of the tap.
If I was picking the plants I think I'd use pennywort or watersprite. Both grow fast along the surface, and are big enough to easily remove them if you don't want them. Plants like duckweed are almost impossible to get rid of once it gets into a tank.
BTW, because these plants do grow fast, they are often considered a "noxious weed". If you live in a warm climate, make sure it's legal to own the plant, and always dispose of any plant removed properly.