Okanagan Koi & Water Gardens

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Gas Bubble Disease

Updated: Fri, 9 Mar 2018

The very rare gas bubble disease...it does happen. How to prevent it.


By: Dayleen Van Ryswyk aka “The Koi Lady”

A few years ago, I got a phone call from a customer that would start me on a path of discovery. The customer had noticed odd behavior with her Koi and weird blister like areas on them. The fish seemed frantic and so did the owner as she tried to understand what the problem was. She described the problem as air or fluid filled blisters on her Koi. The blisters were on the fins and bodies of the fish and seemed to be causing distress in her fish. She said that all the Koi in the pond were exhibiting the same symptoms and that it had just come on suddenly. Their water tests for PH, nitrite, nitrate, KH, GH and ammonia were all good and that they hadn’t done anything recently to the pond that could explain the problem.

From the description of what she was telling me, it sounded to me like a very rare affliction called gas bubble disease. To me, it sounded like gas bubble disease but the odds of it happening are like winning the lottery… slim to none. I made an appointment with her for later that day and went to see the fish for myself.

When I got there, I saw a pristine pond with 10 or so large Koi all up at the top of the water. When I walked over to the pond edge all the Koi came right over to me as if begging for me to help them. They literally had a look of desperation on their faces. The owner couldn’t believe that the Koi all came to me as this wasn’t their normal behavior with strangers. As the lady had said, all the Koi had blisters on them, all of them looked like they were in pain and some of them had the blisters so bad it made the fins look as if they had fin rot. They did indeed look bad, very bad!

I asked her and her husband to show me their filtration. They both looked perplexed and asked me why. I told them that I suspected their filtration and pump could be the cause of their problems. The husband just rolled his eyes at his wife and gave her this “who the heck is this woman you called” look. He proceeds to tell me how he is very diligent about his pond and filtration and that everything was pristine, basically, what the heck did I know about anything anyway. Who was I to question his state of the art set up. I wasn’t there to knock his filtration, I could see everything was immaculate and well maintained, that wasn’t the question. What I wanted to see was “what type” of filtration did he have. When I went around the corner to where the filtration and pump was, my suspicions were validated.

The pond owners had a pressurized filter and a centrifugal pump. Nothing is wrong with that type of filtration; in fact, I have pretty much the same thing on all 9 ponds I have. It’s a great set up and I love it but under certain rare circumstances, it can cause gas bubble disease. When I asked the gentleman if it was at all possible for him to have even just a tiny pin hole in the suction end of his filtration, he outright rejected the notion. The reason I asked the question, wasn’t to suggest that he had done something wrong or that his set-up wasn’t perfect. What the problem was, I thought, was that because they have a pressurized system and an out of the water pump that there could be a pin hole sized hole in his suction line which was letting air into his system. Anyone that has a pressure filter such as a sand filter knows that it’s a nightmare if you get air into the system as it will make the entire system lose its prime. Basically it gets an air bubble in the lines or filter and it won’t flow or run until you get the air out.

When I first arrived, I observed a few things as I stood pond side watching their fish. I noticed a couple of things that would be bad in combination with a pressurized filter system. First, there wasn’t a different source of aeration in the pond other than the filtration. Second, the return line for the filter was below water level. If there in fact was a tiny pin hole in the suction line, it wouldn’t be enough air to shut down the system, so it would therefore go un-noticed. However, it could be just enough air being injected into the system to cause a super saturation of gases within the pond water to cause a rare event like gas bubble disease.

Because their waterfall was shut down for the winter and they shut off their air pump AND because the return water line was below the water level, the gases created by the air injection could not escape the water. They had inadvertently created an environment super saturated with gases that couldn’t escape because there was no surface agitation. What was happening to the fish is pretty much what a diver would experience if they came to the surface to quickly while diving, they would get what’s called the bends. It’s extremely painful and life threatening to divers and would be to the Koi as well. The blisters all over the fish proved this theory to me but now I had to convince the owners that this is what was going on. The problem with my theory was the fact that it was extremely rare, I have never seen it (until now) no one I know in the Koi community had ever seen it, and I’m talking about people that have been in this hobby for more years than I’ve been alive and where Koi are their life and lively hood. People have heard of it, but no one I could find had seen it firsthand. No one could confirm my thoughts.

On a hunch, I thought I would give a Doctor of biology with the fisheries a call and see if he knew anything about this problem. I’m not usually a very lucky person, I have never won more that $86 on the lottery but 2 minutes into my conversation with this gentleman made me feel like I had won the lottery that day. He had just the day before returned from Eastern Canada because of a situation with salmon dying at alarming rates. What they had discovered at a salmon farm was exactly what was happening with my customers Koi; they were covered in blister like lesions. He asked me to send him some pictures by email and that he would let me know right away if it looked the same.

Not 5 minutes later, he called to say he agreed with my diagnosis of gas bubble disease and that I should get the customers to increase the aeration in their pond by any means possible. He suggested that if that was done quickly enough that it should reverse its self fairly quickly and the fish should make a full recovery. I hung up the phone and gave a big hoot and a sigh of relief. I was ecstatic to finally have a 100%, yes; its gas bubble disease second opinion from an expert in the field.

I called my customers right away and told them what the Doctor of biology had said and what they should do to correct the situation. In the end, they lost one Koi to the disease. I was sad to lose the one Koi but the owners were just happy to not lose them all and I guess that’s the better way to look at the situation. Maybe not dwell on the one lost, but the ones saved and the lesson learned.

About a month later, I got a phone call from the ladies husband. He wanted to thank me for coming over and taking the time to figure out the problem but he also wanted to let me know that he discovered something with his filtration. Apparently, my words about a possible pin hole in his suction line nagged at his thoughts to the point that he took his entire system apart. What did he find you ask….a very tiny area in a fitting that wasn’t glued together as well as it should have been. Seems it was sucking in air all along. I appreciated the knowing I was right but it was a lot more than that, I thought it took a special person to come out and admit something at the expense of their own humility.

The lesson to be learned by this story whether you have a pressurized filter system or not, is this. Your water surface needs to be agitated to de-gas. This is so important right now with people winterizing their ponds. I have said it many times before and this story makes it worth repeating. Just having a de-icer in your pond will not keep your fish alive over winter. It may work for a few years but as gasses build up in your pond from decaying debris, Mother Nature will catch up with you and you will lose fish. The water cannot de-gas unless the surface is agitated. It’s that simple! Put an air source beside your de-icer for proper winterizing. If you have a pressure filter, be sure to have the return line above water level so the splashing can de-gas the water.

Even if you have been keeping fish in ponds for 50 years and think you know everything there is to know….you’re wrong! Mistakes happen to everyone, whether you’re a newbie or an expert. Keeping an open mind, asking for advice and learning how to take it, is something we should all strive to do.