By Stephen M. Meyer
Q. I've raised tropical fish for many years. Now I am thinking about branching out into pond keeping. My plan is to dig a 2400-gallon pond in my backyard. Our municipal water has a very high chlorine level. I'm not sure what it is, but you can smell chlorine whenever you turn on the tap. When I do water changes for my tropical aquarium I let the water sit in two 5-gallon buckets for a few days before adding it to the tank.
Although I could use 80 such buckets to dechlorinate the tap water for a 10-percent weekly water change for my pond, it is obvious that this is not the way to go. How do I dechlorinate my pond water?
A. Chlorine is harmful to pond fish and other pond life. The sensitivity of fish to the harmful effects of chlorine depends on a number of variables, including fish species, the organic load in the water, pH, temperature, length of exposure and dissolved oxygen concentrations. Carp (koi) face certain death after eight hours exposure at 4 milligrams per liter (mg/l). But substantially lower concentrations can be lethal if exposure continues over a longer period of time.
Chlorine persists longer in cool and still waters, and dissipates rapidly in warm, churning waters. So spring and fall water changes may pose more risks than mid-summer maintenance.
Clearly, then, it is as important to manage chlorine concentrations in new water added to ponds as it is in aquarium maintenance. As your question implies, if one approached pond water dechlorination in the same way it is done with fish tanks it would be a daunting task. Fortunately, ponds have a few characteristics that make this task a bit easier.
Chlorine levels in municipal systems at the tap can run anywhere from 0.1 to 1 mg/l. By comparison, the highest concentration of chlorine that has failed to show a measurable harmful effect on fish is about 0.02 mg/l. Most fish health specialists recommend that chlorine concentrations not exceed 0.05 mg/l for more than 30 minutes per day; nor should average ambient levels exceed 0.003 mg/l. So these numbers set some boundaries for us to think about.
When dissolved in water, chlorine exists as hypochlorous acid. When the pH is around 6.0 or lower, about 95 percent of the chlorine exists in this acid form. In contrast at a high pH, over 9.0, about 95 percent of the chlorine exists as hypochlorite ion. The hypochlorous acid form is more toxic than the hypochlorite ion form. What matters is that you understand that chlorine is more toxic to fish and other aquatic life as the pH decreases.
So what does this mean for water changing? Assume that the chlorine concentration coming out of the tap is about 0.5 mg/l, that your 2400 gallon pond contains virtually chlorine-free water, and that you want to do 10 percent weekly water changes.
Diluting 240 gallons of fresh tap water containing chlorine (at 0.5 mg/l) in 2160 gallons of "old" pond water produces a final concentration of 0.05 mg/l — presuming thorough mixing. Based on the guidelines noted above, this would seem to be too high.
However, pond water will have a much higher concentration of suspended and dissolved organic matter compared with an indoor aquarium. Levels of phytoplankton (algae suspended in the water), for example, are dozens of times that of a well-maintained aquarium. This organic matter will take up much of the chlorine very quickly. Therefore the fish may only be exposed to harmful concentrations for a short period of time.
If the chlorine is merely in the form of a dissolved gas, you can further reduce the concentration entering the water by spraying the water through the air, rather than just letting it enter the pond from a hose. Spraying dissipates the gas. This will not work, however, if it is chloramine, not chlorine.
You will notice that the animals definitely react to the new water. They will avoid the chlorinated water, and many begin jumping and flashing. Then, too, freshwater aquatic invertebrates are much more sensitive and may die off even after pond organics have reduced the chlorine levels. This can alter the biology of your pond, including affecting the biological filtering action.
Now consider tap water chlorine concentrations that are around 0.1 mg/l. Mixing this in your pond will produce a diluted concentration of 0.01 mg/l. This is probably acceptable for the fish (and perhaps even for other pond life). Again, spraying the water over the pond will cut chlorine levels.
Given the number of uncertainties I have mentioned, the first thing you need to do is find out what the true chlorinating levels are exiting your tap. Call the local water authority and ask for the chlorine concentration target they set. Be sure to ask if they vary the target by season.
Also find out if they use chlorine gas or chloramine. Chloramine is used instead of chlorine in some municipal water systems, and is more deadly than chlorine alone. As already mentioned, chloramine will not dissipate into the air as readily as chlorine does.
Next, purchase a good chlorine test kit and test your tap water. It makes sense to test your tap water daily for a few weeks to get a good reading of average chlorine levels. Chlorine levels also vary by season, so I would test for a few weeks every couple of months.
Then do a little calculation to see what the diluted chlorine concentration will be. Take the measured chlorine concentration, say 0.8 mg/l (or parts per million) and multiply it by the total volume of the new water to be added (in your case, 240 gallons). Then divide that number by the total volume of the pond (2400 gallons). In this case the result is 0.08 mg/l because you are doing a 10-percent water change.
Now you have to decide whether you want to risk adding raw tap water to the pond or use a dechlorinating aid. There are no firm rules. There are a number of commercial products on the market, and their marginal cost is really quite small compared to all the other elements of the pond: fish, fish food, electricity for the pump, etc.
I would suggest erring on the side of caution. Pond fish, such as koi and goldfish, should live decades if properly kept.
Moving Goldfish
Q. I am going to be moving soon. I will be breaking down my 55-gallon goldfish tank and hauling its occupants a couple of hundred miles. I have five large black moors that I've had for six years, and I'm nervous that they won't make it. What is the best way to transport them?
A. This sounds like a pretty easy move, so don't be too nervous. First, go to your local aquarium store and see if you can get them to either give you or sell you 10 large plastic bags for transporting fish. I am sure you will have no problem getting these.
Next, pick up five cardboard boxes just big enough to each hold one bag half-filled with water. The box should be shaped so as to contain the bag in a way that creates a depth of water just over the top fin of the fish. Also, pick up some non-iodized salt.
A few days before the move do a standard water change in your aquarium. Fill one of the bags to create enough depth to cover the fish, but not exceeding 50 percent of the bag's volume. This maximizes the surface area between the water and the air in the bag, allowing for good gas exchange. Now pour the water into a bucket to measure the approximate volume.
On the day of the move prepare a double-bag to hold each fish — just put one bag inside another. Then fill each double-bag with one-third tank water and two-thirds fresh water (dechlorinated). Again, the bag should be no more than half full, with enough depth to cover the fish.
Add enough salt to create a 0.2-percent solution, roughly 1.5 teaspoons of salt per gallon of water. Salt has been shown to significantly reduce transport stress. You might also add a half dose of ammonia remover to the water.
Now scoop your fish from their tank using a plastic bowl so they remain suspended in water. Do not yank them out in a net because this scrapes off their protective slime coat. Gently release them into their individual bags by pouring them out of the bowl. Blow air into the bag to puff it up and then tie the top closed. Close the boxes.
When actually transporting the fish keep them as cool as possible and keep direct sunlight from getting to the boxes. The cooler the fish, the slower their oxygen consumption and production of ammonia. In warm weather it might be worth transporting at night. Some people put one of those small refreezible artificial ice blocks in each box to cool down the water. (But do not let it touch the bag directly — wrap the ice block in a towel.)
When you have your tank set up at your new home, add salt to the water as recommended above. You can reduce the concentration of salt over time as you do water changes.