Besides the classic black beard algae and beard algae, other members of the red algae group sometimes appear in the aquarium as well, though less often. One example is the so-called frog spawn algae, which we want to introduce in more detail in this article. You can find more general information on the topic of "algae" here.

To identify frog spawn algae, you need a good eye or a magnifying glass, since it can easily be confused with other red algae in the freshwater aquarium. This type of algae usually sits firmly on decoration items such as stones and driftwood and has a grayish color. While black beard algae look very bushy by comparison, beard algae are very easy to confuse with frog spawn algae. Both have a similar color tone and elongated filaments. However, Batrachospermum sp., the frog spawn algae, is considerably finer and more heavily branched. By comparison, long beard algae filaments also grow in noticeably more curved shapes.

On closer inspection (and especially when magnified with a macro lens or even a microscope), Batrachospermum sp. shows distinct "knobs" along its branches. Their arrangement, like beads strung on a string, is somewhat reminiscent of frog spawn, which probably also led to the colloquial name of the alga. Frog spawn algae also feel quite slimy, which reinforces the association with frog spawn even more.

In the close-up, the knobs are much easier to see. Copyright by D. Hupfeld.

Common causes of frog spawn algae

In the wild, frog spawn algae are much more common, whereas in the aquarium they appear rather rarely. As with other red algae, a nutrient imbalance can favor the growth of this alga in a planted aquarium or aquascape. This often includes an oversupply of trace elements, especially iron, which usually comes from too high a dose of complete iron fertilizer in the aquarium. If there are too few macronutrients (NPK) relative to iron, this can also favor the appearance of red algae in the aquarium. If frog spawn algae or other red algae appear more frequently, the fertilization should be adjusted accordingly.

Measures against frog spawn algae

Frog spawn algae can be removed mechanically quite easily, since they are anchored to the surface much more loosely than, for example, black beard algae or beard algae. This type of algae can therefore simply be removed by pulling it off by hand or with tweezers. Floating fragments and bits should preferably be vacuumed up with a hose as soon as possible, so that the remains are not spread through the aquarium by the current and then keep growing elsewhere.
Like the typical red algae in the aquarium, frog spawn algae can also be treated well locally using the fogging method with Easy Carbo (instructions are available here). However, this alga responds much more slowly than, for example, beard algae, which turn white or pink quite quickly and then die off. Treatment with hydrogen peroxide (H2O2) is also conceivable.