Fish died after algae treatment

Quail_ChickJuly 11, 2013

Hi everyone,
I have a roughly 1700 gallon, two tiered pond with a waterfall and aerator that I treated for string algae late yesterday afternoon. This morning my husband found one of our 6" comets dead. Yesterday afternoon at feeding time, she was happy, active and feeding, and when I did an autopsy this morning, there were no signs of injury or illness at all. Gills still reddish, no fungus or skin wounds/infections, scales intact, no parasites, lots of food in her gut, swim bladder inflated, no telltale streaking of a systemic infection, etc. All of our fish get annual external parasite checks and we have never had an issue with flukes or other nasties. It's like she just died with no identifiable cause.

We had a total of 3 comets plus 8-9 of their babies from this spring (all under 2"), 8 koi, and various frogs and snails in the pond. It's heavily planted with anacharis, and water hyacinth, and water parameters are perfect. pH 7.6, Ammonia 0, Nitrite 0, Nitrate 0-5. Water is clear and plants are growing very well. Water is well aerated, and no other fish are showing any stress or sickness.

However, we did find one very odd thing in the bottom of the upper pond yesterday, where our DOA lived. We found a mostly picked clean squirrel skull. There were no other bones or evidence that a whole squirrel fell in, and the water is shallow enough that, (a) a squirrel could have gotten out on its own, or (b) we would have seen something before now, or (c) rotting squirrel would have produced an ammonia spike during the weekly chemistry tests. So how the heck did a squirrel head end up in my pond and could this have contributed to comet's demise?

I am thinking it may have been O2 depletion in the upper pond overnight from the algae treatment since it is quite shallow. Does anyone have any other thoughts on what could have caused her to die so suddenly?

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My friend lost all of her fish after treating to algae. I think it was due that she has the majority of the bottom of pond covered with slate and the waterfall didn't push enough oxygen under the slate. So it sounds reasonable to say that your fish died from lack of flow. I don't know from my own experience. The squirrel skull could have been dropped by a bird or dragged by a cat..

    Bookmark   July 11, 2013 at 1:46PM
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sleeplessinftwayne(z4-5 IND)

Algae treatments are rarely beneficial for the fish. They do seem to use up oxygen. If this was one of your larger fish it is almost certainly the problem. String algae is better handled by collecting as much as possible with a toilet bowl brush and pouring hydrogen peroxide such as available at the drugstore directly on the remainder. It is as safe as it gets. You can reduce the water flow temporarily to lengthen exposure time but it breaks down very rapidly. It does not decrease oxygen. I use 1 pint per 1000 gallons. It can be repeated in a matter of hours if your water parameters are good.

Since the algae treatment was the last thing changed and you have eliminated critters and its not likely the skull landed on the fishies head, I have to lean to the treatment as the cause but you know it may not be the absolute answer, just the most probable.

You sound like good ponders. I would enjoy hearing more about your pond.

    Bookmark   July 12, 2013 at 3:20PM
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The best way to cure and algae problem is with more plants. Cover 60% of your waters surface with water lilies and your problem will soon disappear. Also try more oxygen producing plants. It work without any use of harsh chemicals and it is safe and healthy for the fish and they will love you for it.

Here is a link that might be useful:

    Bookmark   July 17, 2013 at 12:08AM
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