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Sexing Koi and Clearing Green Water

Male vs. Female Koi

Adult females are broader, deeper-bodied, especially when viewed from above. Males are slimmer, more torpedo-shaped. During breeding season, males develop rough tubercles on pectoral fins and gill plates.

Green Water Control

Few fish, lots of plants (60% cover).
Good mechanical + biological filtration.
Beneficial bacteria (weekly).
Barley straw (continuous).

Resources

Koi sexing: fishpondinfo.com/koi.htm
Algae control: fishpondinfo.com/plants/algae2.htm

Pond and Water Gardening: Koi Pond Basics: Depth, Filtration, Winter Care & Feeding; Fish Hiding After Predator Visit: Recovery Timeline & Protection; Goldfish Huddling at Bottom for a Week: Predator Pressure & Cold Water Effects; Overwintering 32 Baby Koi: Indoor Tank Sizing & Long-Term Value; Koi and Goldfish Jumping Out of Pond: Causes and Fixes; Koi vs. Shubunkins with Water Hyacinths: Salt and Stocking; Sizing a Temporary Pond for Young Koi and Planning a Permanent Home; Stocking and Winterizing an 80-Gallon Pond for Goldfish; Koi and Goldfish Jumping After Pond Rebuild: Water Quality Shock; Koi Dying, Goldfish Fine: Red Worms in Filter, New Pond Syndrome

Garden Articles

Comet Goldfish and Bullfrogs: Can They Coexist?

Building a Koi Pond: Depth Requirements and Planting Water Lilies

To Run or Not Run a Waterfall in Winter: Koi Survival in a Shallow Pond

Black Water in a New 4,000-Gallon Koi Pond: Causes & Concerns

Adding a Second Koi to a 2,000+ Gallon Pond with Goldfish

Fuzzy Snails and Dying Large Koi: Water Quality Crisis in a Deep, Small Pond

Ulcers on Goldfish and Koi: Aeromonas Infection and Treatment

Plants

Fish Lying on Side at Pond Bottom: What to Do

Spotted Catfish in a Koi Pond: Predator Risk, Not Cleaner Crew

Dropsy in Koi: Emergency Salt, Plant Removal, and Water Quality

Ghost Koi & Goldfish Compatibility: Behavior, Stocking & Predator Awareness

Adding Goldfish to a Large Koi Pond: Compatibility and Filtration

Goldfish Winter Deaths in Kentucky: Pump Failure

Stocking a 50-Gallon Patio Pond: Goldfish and Koi Limits