Oops, My Fish Are Dead…Chlorine Kills

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If I had to summarize the topic this week it would simply be that “chlorine kills fish”.

Not a happy topic to be sure but it’s a reality that sometimes mistakes happen.

If you have a fish pond you’re likely well aware that municipal tap water is not ideally suited to fish health.

Most tap water contains disinfecting chlorine and chloramines, both of which are quite toxic to fish, so when you refill a pond or add water to replace losses from evaporation, it’s a common practice to use dechlorinating tablets or liquids to neutralize these substances.

But not everyone may be aware of this fact or remember to use them.

A long time customer wrote a few weeks ago that she had a friend helping to take care of her pond during a time when she was unable to do so. She got a call one day from her friend that her fish were not looking very well and within a few days, all of her fish were dead.

In the end, she discovered that her friend had added water to the pond but did so without using any dechlorinator whatsoever and as a result, some very large, beautiful, and vibrant koi were lost. It was simply heartbreaking to hear about this and no less devastating to experience it.

Which leads me to an important reminder: Be diligent, not only in your own routine chores and processes as you manage your pond (because we all can make a mistake now and then), but also be thorough in training and guiding someone who’s offered to help you care for your pond. Don’t assume that they understand the various aspects of pond and fish care…it’s simply too risky.

How To Avoid Chlorine Contamination

After hearing about my friend’s loss, we traded emails in which she asked about a way to avoid something like this in the future. It then came to mind for me to suggest the use of a dechlorinating filter which goes on a standard garden hose. Of course she asked if we carried one and I sadly had to say no. But this led me down a path of researching the possibilities to find a good supplier who could produce a great, easy to use filter, at a reasonable price.

I’m now happy to say we’ve found one that makes removing chlorine very easy.

This dechlorinating filter removes all detectable traces of chlorine and chloramines, as well as heavy metals, and a number of other undesirable substances that you might find in tap water. (It works great on well water too). By using this filter routinely when you refill a pond or add water to a pond in the summer, you virtually eliminate the risk of chlorine toxicity (and other contaminants) from entering your pond…and that’s very good for your fish.

To learn more about this filter simply watch the video below or click here for more information.

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9 thoughts on “Oops, My Fish Are Dead…Chlorine Kills”

  1. Thia makes complete sense, and as a precaution is very good advice. I mean, we do it in our fish tank right?

    I guess I’ve been lucky, or my fish are especially hardy… because during the Spring cleanout we all but emptied our 10,000 gallon series of ponds and streams to remove sludge and algae buildup. We then refilled with (treated) well water. No fish problems.

    I’ve been told that normal faucet water,left out, will have a majority of the chlorine evaporate within 24 hours?

    We also have a float fill system (think back of your toilet fill process) that trickles all the time to keep water levels topped off… and no de-chlor process in the loop.

    Our pond system is in full sun, streams are shallow, and some basic rock based algae is resident. I guess that all helps de-chlor?

  2. Hi Steve,
    I’ll take luck now and then:)

    Seriously, you’re correct on the chlorine…it will dissipate within about a day or two so if you’re refilling and have your fish in a holding tank, you should be fine after that time (test the water first) Chloramines however are different. They are used pretty routinely by municipalities and they tend to last for days so those are the ones you need to probably check for, or ask your city water department what they use in their treatments.

    If you’re just adding a trickle in a larger pond your chlorine is likely so diluted it wouldn’t cause much of an issue…everything is probably relative in the sense that fish can and have survived on water additions with some chlorine in it…but everything has it’s limits and I’m not prone to taking many chances (after making a good number of mistakes of my own in the past)

    Thanks for your comments…I appreciate it.

  3. Just wanted to post this email from Midge…great precautionary advice.

    We also lost most of our large, 7 year old koi last summer and I thought this too might be a helpful hint for other pond enthusiasts.

    We have a biological pond and use no chemicals. Last spring my husband sprayed 4 Leland Cypress trees in our yard. They are about 50 feet from the top of our 55 foot creek that drops into our pond. Our fish began to die, one by one. It was heartbreaking and not because they were nice, big koi but because they were members of the family.

    We finally deduced that the spray “floated” down and into the water. Never again will we spray anything around the pond. I had to treat and replace most of the water over a few day period. We added new small koi this year and then were gifted with our own recently discovered babies. My husband is handing our cigars !!!

  4. Can I use bleach in my pond without hurting the pump. I do not have fish or plants. If so how much can I use and how often. Pond size about 400 gallons

  5. Hi Nancy,
    I’m not normally in favor of it but with no fish or plants you could use some bleach and probably be ok. I’ve heard mixed reviews on whether it will damage pump or not. I’ve never used it so have no first hand experience. If I had to guess it’s all relative in the sense that a small amount of bleach probably wouldn’t hurt to try. How much? I would add a bit until you clear up what you’re trying to manage but do it in small increments to keep it minimal.

    There are some reports of people having the seals (rubber) on their pumps ruined by using high levels of bleach so that’s something to be aware of. At the same time I’ve heard of people using it and not having any problems at all. It probably ends up depending on the amount, the duration of use, and the pump in question. The other option would be to contact the manufacturer of the pump directly and get their opinion.

  6. I have hanging poted plants above my pond.
    Is there a fertilizer that is safe to use incase water flows thru the pots and into the pond?

  7. Mark,

    Can you suggest a way to rid my farm pond of lillies? They are taking over the entire pond. We do have fish in the pond and do not want to use any product that is detrimental to the fish. Please help. Thanks.

    Jim Lindley

  8. Hi Brian,
    I think I answered this via email but just in case, I don’t like to fertilize to much in any regard. If there is a chance that this nutrient rich additive will get into the water it will definitely work against limiting algae growth. The plants on the other hand, if they can pull nutrients from the water in some way, will only help.

    All the best,

  9. Hi Jim,
    Generally speaking manual removal might be best, but for treatments, Shore Klear has been used successfully. I would do a bit of research on that and see what you come up with in terms of whether it would fit your comfort zone or not.

    All the best,

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