We have to be willing to change. To rethink. To reevaluate. Over the past few weeks, that’s exactly what I’ve been doing — and I’ve come to a conclusion I didn’t expect.
As many of you know, I have never been a fan of hobbyists routinely salting ponds. My reasoning was simple and practical. Most hobbyists rely on garden hoses for water changes. When a serious issue arises — one that requires a formalin and malachite green (FMG) treatment — you now have a problem. FMG requires salinity to be reduced below 1 ppt, and performing rapid, large water changes with a hose is difficult at best.
The systems I managed for decades were different. Four-inch bottom drains. Two-inch inflow lines. I could flush tanks quickly and safely. Because of that, salt was never an obstacle for me. But I’ve always based my advice on what I would personally do, not theory. That principle has been the foundation of my company and my teaching style.
For over a decade, I worked in Northwest Florida as the General Manager of one of the largest koi farms in the country. Cold water simply wasn’t something I dealt with often. Water temperatures rarely dropped below 50°F, and when they did, it was brief. That experience shaped my perspective — perhaps too narrowly.
Today, I’m no longer just managing large commercial facilities. I’m advising koi keepers across the country and around the world. That requires me to step outside of my own environmental bubble and confront situations I’ve never personally lived through.
Over the past two to three weeks, I’ve watched an increasing number of reports of koi losses in cold water — from my group and many others. These weren’t neglected fish. These were ponds with apparently healthy koi, suddenly keeling over. So I started breaking it down logically. Depth? A 48-inch pond should be better than 24 inches — yet fish in deeper ponds were still struggling. Construction? Above ground vs in ground — no consistent pattern. Mud ponds, natural lakes, artificial koi ponds — all environments koi survive in. Yet the common factor kept pointing back to prolonged cold water and closed systems.
I don’t yet have a definitive answer for why every one of these fish failed. But I do know this: cold water exposes physiological stress that we often underestimate.
Let’s Talk Koi Physiology
Roughly 30% of a koi’s total energy budget is used for osmoregulation. Koi blood sits at approximately 9 ppt salinity. Freshwater is constantly trying to enter the body, forcing the fish to actively pump salts back across the gills while producing large volumes of dilute urine. This process never stops — even in winter. This is also why not feeding during winter does not mean water quality issues magically disappear.
Now consider this: if pond water is held at 3 ppt, the osmotic gradient is reduced significantly. That means the fish is no longer fighting the water chemistry as hard just to stay alive. Realistically, this could free up 10–15% of the koi’s total energy — energy that can instead be used for immune function, tissue maintenance, and basic survival during torpor. From a physiological standpoint, that’s a no-brainer.
My hesitation was never about the science. It was about integrity. I don’t like telling people to do things I’ve never personally done. But refusing to adapt simply because something is outside my original experience isn’t integrity — it’s stubbornness.
So What Would I Do Now?
If I lived in a cold climate. If my pond could freeze. If my fish experienced long stretches of torpor. If my water temperature stayed at 42°F or below for extended periods. I am now convinced that salting the pond can only benefit the fish. I see no meaningful downside in these conditions.
For cold-climate koi ponds, my recommendation is to salt to 3 ppt (3 pounds of salt per 100 gallons). This is not about treating disease. It’s about reducing unnecessary physiological stress at a time when koi are least able to handle it.
Sometimes the most important thing we can do — for our fish and for ourselves — is admit that it’s time to rethink old positions. That’s where I am now.
Going into a hard winter? Learn more about why koi die in winter and the right way to use salt in our salt bath vs dip guide. Need pond-specific advice? Book a koi health consultation.
Written by Jason Michael, a 30-year aquaculture professional with experience in commercial koi farming and fish health management.
