Algae Management for Medaka Keeping — Working with Green Water Effectively

When raising medaka, green algae can grow on the walls or bottom of the container, or the water can turn green in what's called green water. Algae is not necessarily harmful to medaka, but it can diminish the appearance and, if it grows excessively, can cause water quality deterioration. This article explains the types of algae, countermeasures, and how to utilize green water.

Types of Algae That Occur in Medaka Cultivation

There are mainly four types of algae species that appear in medaka cultivation. Green algae is thin green algae that adheres to the walls and bottom of the container and is the most common. It naturally develops if there is light and nutrients, and in small amounts can become food for medaka. Aominudoro is thread-like green algae that forms fluffy clumps in the water. If left alone it multiplies explosively, and medaka can become tangled and unable to move, so early treatment is necessary. Blue-green algae (cyanobacteria) forms a bluish-green slimy membrane and has a distinctive odor. It's a sign of water quality deterioration; remove it promptly if found. Green water is a state where plant plankton (such as chlorella) proliferates in large quantities in the water, making the entire water green. Although it looks unappealing, it has many benefits for medaka cultivation.

How to Utilize Green Water

Green water is a "universal water" with many benefits in medaka cultivation. Plant plankton in the water serves as food for fry, dramatically improving fry survival rates. For adult medaka, fine food is constantly floating in the water, contributing to nutritional intake. Since plant plankton absorbs ammonia and nitrates from the water, it also has a water-purifying effect. Reports also show that medaka body coloration becomes more vivid, with this tendency being especially pronounced in red-colored varieties. To create green water, place medaka cultivation water in a sunny location and dissolve a small amount of food in it; it will turn green in a few days. However, excessively concentrated green water risks oxygen deficiency at night, so if the water is so concentrated that the bottom is no longer visible, add fresh water to dilute it.

Prevention and Removal Methods for Algae

The basic principle of preventing algae is controlling "light" and "nutrients." In environments where direct sunlight shines for long periods, algae increases rapidly, so blocking afternoon direct sunlight with a shade cloth or light-blocking net is effective. If the amount of food is too much, nutrient levels in the water increase and cause algae, so aim for an amount that can be consumed in 2-3 minutes. Green algae adhering to the container walls can be easily removed with a melamine sponge. Aominudoro should be removed by wrapping it around wooden sticks or a toothbrush. If treated while still small, it finishes quickly, but if it has grown excessively, a reset (complete water change and container cleaning) may be necessary. Blue-green algae can be removed by locally applying hydrogen peroxide or by complete darkness for 3 days. Regular water changes (once a week, about one-third of the total) are also fundamental to algae prevention.

Utilizing Algae-Eating Organisms

Using algae-eating organisms together with medaka is also effective. Minami shrimp are small Japanese shrimp most suitable for co-habitation with medaka. They eat green algae and aominudoro on the walls, but since their algae removal ability is not that high, consider them a supplementary measure. Nerite snails are reliable organisms that efficiently eat algae on walls. However, the drawback is that they lay eggs on walls, which don't hatch in freshwater, leaving white egg marks. Pond snails have the ability to filter-feed on plant plankton in the water and can make green water transparent. Be careful not to add pond snails to containers where you intentionally want to maintain green water. Yamato shrimp have high algae-eating ability but are large-bodied and sometimes eat medaka eggs, so they are unsuitable for breeding containers.

Setting Up Medaka Breeding Environment with Br-choku

Algae management is a matter of balancing the entire breeding environment. At Br-choku, you can purchase medaka from breeders with extensive outdoor breeding experience and receive specific advice on managing the breeding environment. The benefit of purchasing directly from breeders is obtaining practical information, especially about how to utilize green water and breeding environments suitable for each variety.