Vacuuming the substrate

When doing water changes, it is useful to remove as much dirt and debris as possible, by siphoning it from the substrate. This will help remove physical dirt from the tank, and prevent it breaking down further and adding to waste levels (such as nitrate and phosphate) in the tank.

For gravel substrates, plunge the end of the siphon tube into the gravel to suck dirt out - special gravel vacs (siphon tubes with a wider end piece) are available for this purpose. These allow the dirt to be sucked from the gravel as it is stirred up, the gravel then falls back into place and the dirt is sucked through the tube into the waiting drain, bucket, etc.
For sand substrates, hold a normal width piece of tubing or clean garden hose about half an inch above the surface of the sand, which should pick up visible debris without disturbing the sand.
Vacuuming the gravel is particularly important in tanks with undergravel filters (UGF), to keep the filter bed healthy. Contrary to an old myth, vacuuming dirt from the gravel will not remove all the beneficial bacteria, which tend to live tightly attached to the gravel in 'biofilms'.
In planted tanks, vacuuming the substrate is very difficult, especially if the tank is well planted. However, plant roots themselves will help to keep the substrate healthy, so vacuuming a planted tank substrate is not as necessary, and may even be a bad thing if the roots are disturbed excessively. Also, with certain nutrient substrates, plunging a gravel vac down into the substrate will churn up the nutrient layer, which is likely to cloud the tank and could lead to algae problems due to the nutrients being released in to the water column where algae can make use of them.

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