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Bagging Aquarium Fish and Dechlorinating Pond Water

A reader disagrees about how to add air to a bag containing fish.

By Stephen M. Meyer

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Q. I was going through the July 1997 issue of AFI when I read this department. Stephen Meyer, are you nuts? In response to a question about moving goldfish, you told the guy to put some water in a plastic bag, "blow into the bag" for air, and then tie it up for transport. You were kidding when writing this stuff right?

Remember back in physical science class: breathe in oxygen and exhale...carbon dioxide! I am sure that this guy's fish died in about 20 minutes after following your advice. I think you owe him a new fish for this false information.

I am writing this in detail so you can follow. When you bag a fish you can catch atmospheric air (which contains 20-percent oxygen) in the bag. Or better yet, shoot oxygen from an oxygen cylinder, or pump air from an air pump, or use a commercial oxygen supplement.

One more thing. I hope you don't maintain ponds, because your advice about dechlorinating was wrong. There is a simple solution for dechlorinating pond water when doing a water change (once again in detail so you can follow). Use a Python system hose fitted with a modular filter containing activated carbon. The carbon removes the chlorine and there is no need to worry about the fish.

A. Sorry you found my column so disagreeable. It is true the exhaled air contains a smaller percentage of oxygen and a higher percentage of carbon dioxide (CO2) compared with atmospheric air. The difference, however, is negligible (unimportant) when you blow up a bag for fish for short hauls.

Really, think about it. The rapid breathing that takes place when you blow up a balloon (or give CPR) does not allow for much gas exchange in the lungs. If it was true that exhaled air had dangerous concentrations of CO2, what do you think would happen when you gave CPR to someone? How many people have died from CO2 asphyxiation after receiving CPR?

Yes, an air pump would be a good alternative, but not if you did not have an air pump. Yes, an oxygen cylinder would be a good alternative, but not if you did not have one — or were afraid of a fire hazard. I agree that an oxygen-rich air mixture would be a superior choice for long hauls. But, frankly, opening the bag and breathing fresh air into it a few times would do just as well.

Fortunately, you can tell when bagged fish need "fresh air" because the bag deflates as CO2 replaces oxygen. It loses its tautness.

Fish are most likely to suffocate when the bag contains too much water. The volume ratio of air to water is more important under most conditions. Roughly, the bag should contain no more than 25 percent water. In fact, the great risk to transporting fish is not asphyxiation but 1) ammonia poisoning, 2) overheating or freezing, 3) leaks, 4) physical injury and 5) systemic stress from handling during the move.

Regarding the use of activated carbon for dechlorination, yes, it would work. But first, most pond water changes involve a hefty volume of water on a frequent basis, and therefore a hefty volume of activated carbon to do the job right.

Second, most pond water changes involve fairly rapid flows that would be significantly impeded passing through a carbon chamber. Water changes already take hours in my ponds using 1-inch hoses. Your approach would require a day or more. Third, it really is not necessary in most circumstances. On the other hand, for those who have small garden ponds (say, a few hundred gallons or less) your idea has lots of merit.

Thanks for writing. I think a smart reader should always have a healthy skepticism about the material found in magazines and books. I am glad to see you questioning the advice you read here.

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