06-20-2011, 01:08 PM
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It somewhat depends upon what is going in the tank, fish- and plant-wise.
Substrate fish such as corys, loaches, and several others require smooth substrates. Some gravel and some sands are rough, not good for these fish. Aside from this aspect, some of the substrate fish do better with sand. The dwarf cory species particularly; the medium corys and most loaches may be better in sand but will manage fine in small-grain gravel. The larger pea gravel I would not recommend, having tried this. My loaches are doing much better in fine gravel.
Plants do best in sand or fine gravel. Here again, I have had less success with plants in pea gravel, whereas the same plants thrive in small gravel. The substrate needs to be small-grained both to serve as a rooting medium and to function biologically for a healthy aquarium.
Compaction of the substrate is an issue with sand or gravel, but moreso with sand being finer. However, substrate-rooted plants help to prevent this, as do Malaysian Livebearing snails that burrow throughout the substrate. Keeping a sand substrate shallower than one could with gravel is also advisable. Maximum of 2 inches with sand, whereas fine gravel at the back of the tank can be up to 4 inches if there are large-root system plants like the larger swords.
To the cleaning. Gravel is easy to maintain, with a water changer device. This cannot be used with sand as the sand will get sucked up. You can carefully run the device just above the sand to pick up particulate matter, first stirring the sand with a stick or fork. This assumes no plants.
With live plants, I never touch the substrate. There is a complex biological system at work down there, and I always believe it is preferable to let nature do its job without interference from me. Organics collect in the substrate, and a host of bacteria (different from the nitrifying bacteria we frequently talk about) work to break it down. The plants contribute by providing copious amounts of oxygen through their roots. Oxygen also enters via the water which will be pulled down through the substrate and back up again due to the heat generation by the bacteria. This is another reason for having a fine-grain gravel or larger sand substrate; water flow must not be impeded, but at the same time it must not be too free, as it would with larger gravel. This biological action also helps prevent compaction.
A dark substrate is almost always better, whether gravel or sand. Most of our fish occur in streams with very dark substrates, and a bright substrate makes them uneasy because it is un-natural. Overhead light is also reflected more off a lighter substrate, increasing the problem.
Hope this explains what you asked.
Last edited by Byron; 06-20-2011 at 01:11 PM..