Killer Chlorine

Q. I have been keeping aquarium fish for many years, but the problem I am having with the pond I recently installed in my backyard is like nothing I've encountered before. None of the fish I put in it live for more than four days.

The pond is above ground and constructed of landscape timbers. It measures about 8 feet by 9 feet, and varies in depth from about 16 inches at one end to about 28 inches at the opposite end. I figure about 800 gallons. The ground and timbers were covered with a felt-like pad and then a 40-mil-thick rubber (polybutyl?) liner. The liner extends over the top of the landscape timbers. It's a very shady pond, with large tulip poplars and oak trees shading it most of the day. It has a Beckett "Versa Pond" biological pond filter, which consists of a plastic box holding about 2 gallons of bioballs and a pump. The discharge tube from the pump goes out the top of the box to form a fountain above the water.

I have tried some seven pairs of fish, mostly goldfish — regular and pond comets. None of them lived longer than four days. The pond has been drained and refilled twice, to no effect. The fish show no external signs of disease, but just sit on the bottom of the pond, usually in a corner. This begins about a day after they are put in and continues until they die. The pH is about 7, temperature of the water is about 65 to 70 degrees Fahrenheit, and ammonia and nitrates are low. There have been no fertilizers or insecticides used in the yard. I did spray some weed killer in the general area, but that was two water changes ago, and there is no way any runoff can get into the pond — and I was very careful to apply it on a calm day and with extreme caution near the pond.

I'm stumped, as is everyone I've talked with. Any idea what's killing my fish?

A. On the basis of your description of the behavior of the fish and the time involved, I can say with confidence that no disease or parasites produce this type of problem. When you see rapid and complete mortalities of this type in a new setup you should begin your diagnosis with the assumption that the problem is with the water.

Let's start with the obvious: pH. The pH may be 7, but what was the pH of the water in which the fish were being held? Was it 8.5 or 6.0? pH shock usually causes goldfish to act skittish, darting around the tank. Other times they behave as you describe before they die. Goldfish may be hardy, but pH stock really can kill them — just like any other fish.

You say you have long experience with aquariums, so I presume you have tested for and neutralized any chlorine or chloramine in your water. Chlorine poisoning produces the very effects you describe. The chemical burns sensitive gill filaments, causing the fish to slowly suffocate. It usually takes several days. Perhaps you have just moved to a new area and took for granted that the water did not have chlorine.

Test the water with one of the many inexpensive test kits available. And test of chloramine as well.

Then there is nitrogenous waste pollution. Your letter indicates you tested for ammonia and nitrate. Even 20 large goldfish in 800 gallons of water with a pH around 7 could not produce enough ammonia to kill themselves in so short a period of time. Assuming no biological filter at all, they would produce about 500 milligrams of ammonia per day, which in your pond would result in an ammonia concentration of about 0.2 parts per million (ppm). After five days you would have at most only 1 ppm of ammonia. At the neutral pH you report the amount of toxic ammonia would be less than 0.005 ppm — well within safety limits for long-term exposure.

Nitrate will not harm, let alone kill, goldfish. What about nitrite? Given the fish load in your pond, I cannot see nitrite poisoning as a serious possibility either. Moreover, goldfish usually gulp at the surface if they are having nitrite problems.

I do not believe that weed killer is the culprit, especially after two water changes. Of course if it is a persistent type with a "sticking agent" added, and if heavy rains or watering were able to continually flush it into the pond, then there would be a chance of it repoisoning your pond after every water change. But, in your situation this is rather unlikely.

So, that brings us to the liner. Yes, the liner may well be toxic. The symptoms you describe are entirely consistent with liner-borne toxins. I have seen this several times over the past few years, usually when people try to use ordinary swimming pool liners rather than more expensive fish-grade liners. Non-fish-grade EPDM liners will also kill fish in the same way, and four days is right on the money.

While I appreciate you sending a sample of the liner, unfortunately, I cannot test it for you. If you want to know for sure, do the following: Cut a large piece of liner and place it inside a 5-gallon pail. Fill it with fresh, dechlorinated, water. Add an airstone and place a feeder goldfish in the pail. Do not feed, just watch. You will know the answer soon enough.

Dumbfounded or Just...?
Q. I was dumbfounded when I read your response regarding one fishkeeper's diseased goldfish in the April 1995 column. First, couldn't you have referred her to any number of excellent and inexpensive books on aquarium fish disease?

Second, you never mentioned having ever received a sick fish from her or doing an autopsy on dead ones, if indeed they had died. How did you diagnose? Are you a fish pathologist?

Third, I have never heard of or read about any "swimbladder" disease that is caused by flake or pellet food. Some disease organism would be a far more likely culprit. I say this because I have bred head-and-tail light tetras with a mixture of live foods — grindal worms and fruit flies — and flake foods, which they relish. No disease whatsoever that I've heard of is caused by diet.

Perhaps a better editing job would have lead to inquiries about her fish before you printed your response, which I consider glib and libelous. Don't you think a manufacturer of flake food and pellet food would feel that your response could cause them serious economic damage? How would you answer them if they asked you some questions and pointed out the flaws in your answer as I did? I think if that article is read by the manufacturers you will be up against the wall in trying to justify your negligence in printing that response without questioning the potentially libelous context.

Rest assured that it will be infrequently when I purchase another copy of Aquarium Fish Intl.. Glibness is no substitute for careful, intelligent writing. You have a ways to go before you are an intelligent publication.

A. I have reprinted your letter almost in its entirety because I think it is important for readers to see how dangerous ignorance really can be. Ah...where to start?

Let's work backwards through your points. My answer to the fishkeeper's question was anything but glib. It was based on almost two decades of experience in working with goldfish and koi, diagnosing what now must be thousands of pond fish ailments directly — and yes, including many hundreds of necropsies (I could only perform an autopsy on a fish if I were a fish; look the word autopsy up in the dictionary).

Your most telling point is that you have never heard of any disease caused by diet. Well, how about reading something on the subject of fish disease? Take a look at Post's Textbook of Fish Health, Andrew's Manual of Fish Health, Reichenbach-Klinke's Fish Pathology or Wedemeyer's Diseases of Fish, Book 5. Then there are literally thousands of published articles in the professional literature on fish disease caused by diet. You should not confuse the fact that you do not know something with the assumption that it is not known by others.

Why haven't fish food manufacturers yelled and screamed about my observation? Because they know it is true and is no threat to them. If a goldfish hobbyist calls any of the reputable manufacturers and talks with a technical representative, one of the first suggestions heard will be to soak the food because dry flakes and pellets very frequently create flotation problems for goldfish. Fish food manufacturers cannot be blamed for the digestive problems of mutant goldfish. They are well aware of the problem and, in fact, often refer people to this column for information about the topic.

Although the fishkeeper who wrote the letter does not live very far away, I did not examine her fish, and there was no need to. The problem was obvious to anyone familiar with goldfish. Every goldfish breeder and serious pond fish hobbyist knows how dried flakes and pellets affect goldfish behavior and balance. It is the most common goldfish ailment, and the goldfish literature has discussed it for at least 20 years.

The fact that your tetras have never been afflicted by this problem is not a surprise to anyone knowledgeable in fish anatomy. As I explained in my reply to the fishkeeper, fancy goldfish have very peculiar anatomies because of the artificial genetic selection that is part of selective breeding for shape. That's why they have problems that normal goldfish don't.

Now, perhaps, you can see why I did not tell her to read a book on fish diseases. It would be a waste of her time and never address the problem at hand. So, as I tell my own students, come back when you are ready to learn something.