Originally Posted by grannyfish
How deep do you want a sand substrate to be and will plants root in sand better than gravel?
I just removed most of my new gravel and added black sand but it is not very deep. I have seen many pictures posted where the substrate is pretty shallow. how do the plants root in it if it is only 1/2 in or so deep?
Most plants will root in either sand or fine gravel. Some will do better in sand, thinking here especially of so-called carpet plants which are very small with very fine roots and these find it more difficult in coarser substrates. Some plants have some difficulty, or do less well, in larger-sized gravel, like pea gravel or birdseye. But there is more to this than just "taking hold," there is also the critical issue of organics and bacteria and nutrients. Too coarse a substrate and the water flows through it too quickly, not allowing roots to take up nutrients, making it more difficult for waste to be broken down, etc.
When we look at natural habitats of aquarium plants, we find a majority grow in a mix of clay and sand which is quite a compact material mix. Of course, in nature all this biology behaves differently than it will in a close aquarium system, where compaction can kill the plants and fish. There has to be a balance.
To the depth, this depends upon the plants. I have some large swords, Echinodorus cordifolius and Echinodorus bleherae, and these have immense root systems that extend many inches beyond the crown, and down through the depth. Even so, the depth of the sand in my tank with these plants is no more than 2 to 3 inches. If the sand is only 1/2 inch deep, all but the smallest plants will have difficulty. Most of us tend to have a shallow depth in front, maybe 1 inch, sloped or terraced up deeper in the back where the larger plants will naturally be planted.
You might find this article on bacteria informative, as it goes into the substrate issue: http://www.tropicalfishkeeping.com/f...quarium-74891/