Professor, Texas A&M University
“In the field of aquatic health, success begins with a fundamental understanding of the environment. SECRETS FOR HAPPY KOI translates complex concepts in water chemistry and ecology into a clear, actionable framework. It is a methodically sound resource that provides the everyday koi hobbyists with the diagnostic mindset needed to maintain a balanced ecosystem and prevent disease before it starts.” — Haitham Mohammed, DVM, Ph.D., CertAqV Assistant Professor of Fish Health & Disease Department of Rangeland, Wildlife, and Fisheries Management Texas A&M University
POND Trade Magazine
“At POND Trade Magazine, we value educational resources that elevate the industry and help hobbyists and professionals better understand the living ecosystems they create. This book not only provides practical guidance, but also encourages readers to see their ponds through a more thoughtful and informed lens. Whether you are new to koi keeping or have years of experience, SECRETS FOR HAPPY KOI offers insights that will strengthen your understanding and appreciation of the hobby.” — Lauren Nolan, Publisher, POND Trade Magazine
EasyPro Pond Products
“Rajat skillfully blends scientific detail with practical guidance, making SECRETS FOR HAPPY KOI an invaluable resource for koi enthusiasts. The book reflects his deep expertise and genuine passion for the hobby. His koi pond is both a work of art and a testament to the knowledge, care, and dedication woven throughout every page. This is a book koi enthusiasts will return to as a trusted reference for years to come.” — Matt Meachum, Director of Sales, EasyPro Pond Products, Inc.
Reserve Grand Champion, San Diego Koi Show
“SECRETS FOR HAPPY KOI blends aquatic science with practical application in a way that’s rare in hobbyist literature. It connects the dots between water chemistry, ecology, and koi behavior, offering a framework that’s both rigorous and accessible.” — Gordon Chibana, Reserve Grand Champion, San Diego Koi Show
Pond Owner
“Rajat helped me build my koi pond and taught me more about koi than I ever expected to learn. This book captures everything he showed me — how to actually read your water, avoid the mistakes that cost you fish, and stop stressing so you can just enjoy them. If you want to understand what’s really going on in your pond, this is the book.” — Kris Perez, Pond Owner
President, Kodama Koi Farm
“Rajat’s passion for helping new pond owners enjoy koi comes through clearly in this book. SECRETS FOR HAPPY KOI encourages beginners to think more carefully about water quality, observation, and the responsibility of koi keeping.” — Taro Kodama, President, Kodama Koi Farm
Stonebridge Pond & Waterfall Co.
“Rajat’s passion for koi health and nutrition truly shines through in this book. It’s a valuable resource for koi keepers and pond enthusiasts looking for helpful information, deeper understanding, and practical tips for supporting healthy, thriving fish.” — Eric Arntson, Owner, Stonebridge Pond & Waterfall Co.
Owner, Bristol Koi Farm
“Written with genuine passion for koi and the hobby, this book is a reflection of the author’s dedication to sharing their experience with fellow enthusiasts.” — Parinaz Bristol, Owner, Bristol Koi Farm
President, Austin Pond Society
“SECRETS FOR HAPPY KOI cuts through the noise and explains pond care in a way that finally makes sense. Clear, accurate, and grounded in real-world experience, this is the guide every pond enthusiast should have on hand.” — Barb Lenhardt, President, Austin Pond Society
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Secrets for Happy Koi:
A Definitive Guide for New Koi and Pond Owners

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From Murky to Magical: Understand Your Pond with Science and Simplicity

Koi keeping and pond maintenance are often portrayed as either deceptively simple or overwhelmingly complex. New pond owners quickly face conflicting online advice, vague tutorials, and trial-and-error videos that can lead to unhealthy fish and unstable ponds. Secrets for Happy Koi bridges that gap with clear, science-based guidance that helps koi keepers build thriving, balanced ecosystems with confidence.

Drawing on real-world experience and aquatic science, Secrets for Happy Koi explains not just what to do, but why it works. Topics include koi biology and evolution; pond startup and filtration; water chemistry; algae growth, stages, and control; pond plants; bogs; feeding practices; quarantining; predator management; and common mistakes to avoid. Complex concepts like the nitrogen cycle are made simple: explained well and supported by visual timelines and illustrations.

Whether you’re setting up your first pond or improving an existing one, this practical guide provides the knowledge you need to care for koi responsibly and sustainably—and to enjoy the beauty and serenity that inspired you to keep them in the first place.

This book covers: 

• Water chemistry (the nitrogen cycle)

• Bacteria, algae, and biofilm

• Filtration

• Ideal water quality parameters, what they mean, and what to do when they’re off

• The pond evolution timeline and what to expect at each stage

• Pond plant types and placement, benefits, and invasive and poisonous pond plants to avoid

• Bogs and wetland filters

• Koi metabolism and nutrition

• Feeding guidelines and recommendations based on season and temperature

• Safe and unsafe treats for koi

• Koi anatomy

• Koi illnesses, what to look for and what to do

• How to quarantine koi

• Pond maintenance

• Common mistakes to avoid

• Species that can (and should not be) added to your pond

• Equipment, what it does, what’s essential, what’s nice to have

• Predators and how to deter them

A devoted pond owner since 2004, Rajat Agarwal has a deep affection for koi, appreciating their vibrant colors, unique personalities, and graceful nature. Through more than two decades of hands-on experience, he has developed extensive knowledge of koi varieties, classification, behavior, and care, as well as expertise in pond design and building, Japanese landscaping and garden design, and water maintenance. Agarwal has shared his experience with pond societies in Austin, San Antonio, and Houston, and at the Austin Oita Sisters Japanese Cultural Event. He has been featured on Central Texas Gardener on PBS/KLRU-TV, Studio 512 on KXAN, RJ Designs on KLBJ radio, and in POND Trade Magazine. In 2025, he founded ATX Koi Corp (www.atxkoi.com), the leading supplier of Japanese and domestic koi in the Greater Austin area, offering fish, pond supplies, consulting, and maintenance services dedicated to helping others create and care for their own living works of art.

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