Lexicon: G
Gravel filter | What is a gravel filter?
A gravel filter is a filter used to purify water in ponds and swimming pools. Gravel filters, sponge filters or filter cloths have such large openings that the fine, turbidity-causing particles pass through them. These so-called coarse filters can only be effective when used in conjunction with flocculants (such as aluminium sulphate, for example). These flocculants are stirred into the water and cause the fine, turbidity-causing particles to clump together into larger particles, so that they can be collected. To filter out the finest particles, a gravel filter must be used.