07-02-2011, 10:51 AM
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Originally Posted by leogtr
oh okay that sound good! yeah they do grow fast in small gravel but I was thinking that it did because of the waste of the fish and such that falls in between the rocks and makes a kind of fertilizer for them..
thank you Byron!
That's correct. The plain gravel or sand is itself devoid of any nutrients. Organics (from fish waste, decaying plant matter, uneaten food, dying bacteria, etc) accumulates in the substrate, and a host of bacteria break it down into nutrients for the plants. But this also occurs in any substrate. While some claim that soil quickens this process, it does so at a cost.
You do not want too large a grain size for the gravel; grains around 1-2 mm in diameter are best. Water has to circulate, but the substrate has to be small enough to anchor plant roots and provide a good bed for the bacteria.
The substrate in a planted tank should not be vacuumed, as this removes much of the essential organic matter. Let nature do its thing, it knows best.