Diatoms or brown algae are normally at most a marginal phenomenon during the cycling phase of an aquarium. They often disappear again on their own or are displaced by other biofilms. If these algae are a permanent problem, however, an elevated silicate content may be the cause. Here we show you how to best lower silicate in the aquarium.

The silicate level in the aquarium

Silicates are compounds of silicon and oxygen and represent the salts and esters of silicic acid. The basic building block is an SiO₄ tetrahedron. In nature, these minerals even make up a large part of the minerals found in the Earth's crust.
The concentration of silicate (expressed here as SiO₂) in aquarium water is one of the water parameters that play only a minor role. As a rule, silicate is hardly present in the water, or not at all. Silicates are, however, an important building block for brown algae such as diatoms. They use silicate, more precisely silicon dioxide, for their growth. Their box-shaped cell wall is built from this material.

Diatoms usually only appear briefly in the cycling phase of a freshly set-up aquarium. They often disappear again on their own, because their food supply is soon cut off or other competing algae species and microorganisms spread and then displace the diatoms. If such brown algae, also called diatoms, are a permanent problem, however, an elevated silicate content may be the cause. You can verify this with a suitable water test.

Finding the cause

First of all, you need to find the cause of the elevated silicate content. Very often the source water is already contaminated. You can check this with a silicate water test or, if you use tap water, often look it up in the drinking water analysis of your water supplier. This is quite often posted on the websites of the respective water suppliers.
However, another element can also be the cause of the silicate input. Some natural substrates, such as soil, can sometimes release silicate.

Countermeasures

If diatoms are a greater problem in the aquarium, you should first try stocking suitable algae eaters. Invertebrates such as numerous snail species and shrimp, but also ornamental fish with sucker mouths, fall into this category.

If algae eaters are present in sufficient numbers, they can often push the algae back visually very far. Brown algae can also occur in aquariums that are rather weakly lit. Here, improving the lighting situation can sometimes lead to the diatoms being displaced by other biofilms such as green algae coatings. Whether this is really expedient is debatable, however, since you then simply find green coatings instead of brown ones.

There are various other approaches to removing silicate from aquarium water, which are then solved technically. First, there is the use of a silicate remover as a filter material, such as SilicateEx Rapid from JBL. Many silicate adsorbers, which are often a granulate based on iron hydroxide, however, also remove phosphate compounds from the water, and even preferentially so. In the first place, phosphate is thus bound in the filter material. In a planted aquarium this can sometimes be counterproductive, since the plants then lack an important macronutrient. The filter medium of a silicate adsorber also has to be replaced regularly as soon as it is exhausted and can no longer absorb substances.

An alternative would therefore be to use such a silicate adsorber, but only on the fresh water for a water change. For this, the fresh water has to be treated somewhat. The water is collected in a container that is large enough. You then place the right amount of silicate remover in it to match the water volume and let the water circulate for several days with the help of a circulation pump. Once the silicate has been removed, the fresh water can then be used for the aquarium. This is considerably more laborious, but has the advantage that you do not use the silicate remover directly in the aquarium. Consequently, there is also no lasting effect on the phosphate content, and added fertilizer is not bound by a filter medium either but is available to the plants.

Another possibility would be water treatment built up from scratch. Here, completely demineralized water is produced (for example by a reverse osmosis system with a downstream mixed-bed resin filter), which is then adjusted again to the desired water hardness parameters with a hardening salt. This also takes somewhat more effort, but you can then offer your aquatic plants and aquarium animals perfect water parameters.