Medaka Water Quality Guide

Medaka are hardy fish, but proper water quality management will keep them healthier and longer-lived. Learn the right timing and methods for water changes, plus how to use green water effectively.

Ideal Water Conditions for Medaka

Water Temperature - Optimal range: 16-28°C - Outdoor keeping in spring-fall generally presents no issues with natural temperature changes - Watch for summer heat above 35°C and winter cold below 5°C

pH (Hydrogen Ion Concentration) - Optimal range: 6.5-8.0 (slightly acidic to slightly alkaline) - Tap water pH varies by region but is generally near neutral - In heavily planted tanks, CO2 absorption by plants can cause pH fluctuations

Ammonia and Nitrite - Ammonia from fish waste is toxic to medaka - Beneficial bacteria convert ammonia to nitrite, then to nitrate - Nitrate is less toxic but accumulates, requiring regular water changes

Water Change Basics

Recommended Water Change Frequency - Outdoor containers (no filter): 1-2 times per week, replacing 1/3 to 1/2 of total volume - Indoor tanks (with filter): Once per week, replacing 1/4 to 1/3 of total volume - Green water systems: Every 2-3 weeks (when the green color becomes too dark)

Frequency depends on stocking density and feeding amount. Water that smells bad or turns cloudy signals the need for a change.

Water Change Procedure 1. Prepare new dechlorinated water 2. Match the new water temperature to the tank (within ±2°C) 3. Remove 1/3 to 1/2 of the tank water 4. Slowly add new water (avoid sudden water quality changes)

Dechlorination Methods - Add commercial chlorine neutralizer (liquid or tablet form) at the recommended dosage - Leaving water in sunlight for 1+ day also works - Fill a PET bottle with tap water, remove the cap, and expose to sunlight for several hours

Using Green Water

Green water is water that has turned green from a large population of phytoplankton. It offers many benefits for medaka keeping, especially for fry rearing and outdoor keeping.

Benefits of Green Water - Phytoplankton serves as food for both fry and adults - Phytoplankton absorbs harmful substances (ammonia, etc.) from the water - Provides moderate shading that smooths temperature fluctuations - Creates a calming environment for medaka

How to Make Green Water 1. Place a container in a sunny location 2. Add a few medaka and feed them 3. Water will turn green within 1-2 weeks 4. Adding commercial chlorella solution speeds up the process

Green Water Cautions - Water that becomes too concentrated can cause oxygen depletion (aeration recommended) - Difficult to produce indoors - Since water quality is hard to assess visually, maintain regular water changes

Signs of Water Quality Deterioration

Watch for these signs and perform a water change immediately:

Water Appearance - Cloudy/milky water - Oily film on the surface - Foul odor - Water turning brown or darkening

Medaka Behavior - Gasping at the surface (sign of oxygen depletion) - Lethargy and sitting on the bottom - Loss of appetite

Proper water quality management keeps medaka healthy and strong. Fry are especially sensitive to water quality changes, so attentive care is essential.