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I keep about one third of my pond surface area covered with plants. Over time, some of the leaves die, and fall to the bottom of the pond. Gradually the water has become tea coloured, which I understand is caused by tannins in the water from the leaf degradation (I can't think of the right word just this second!). Apparently activated carbon clears the water.  I am experimenting with just a simple bag of charcoal hanging at the inlet to the pond, which I washed thoroughly before adding.  It seems to be working, my water is slowly clearing. So, this may also be protecting me from any chlorine spikes? Where have any of you sourced activated carbon, which would be even better, albeit more expensive?

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Something bad in the water appears to be the answer.

Did you, or a next door neighbor, spray the yard for critters?  Wind could have carried it into your pond.      Just replace the water.  Let it stand for a couple of days.  Then add a couple of gold fish for a test.

I believe the LCS has a net you can use.  Just bring a container and you can net a couple for a small fee.


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The fish pond expert who volunteers at LCS just came by and raised the same possibility.  We can't find any trace of chlorine or chloramine so we are pursing that avenue of investigation.  Our gardener does use stuff on the lawn to kill the gusanos (grubs) that kill the grass.

We'll start over with better plants and maintenance and also extra care with make up water and lawn chemicals.

Thanks to everyone for your help and suggestions here.  Much appreciated!


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On 2/8/2017 at 5:25 AM, Ukiyo said:

Goldfish (Kingyo) and Koi are very popular in Japan, and here are some tips which I have been told locally;

1) Change 1/3-1/2 water with new water without chlorine regularly, say once a month. This is to lower Nitrous acid and ammonia in the water. Check PH concentration too. Aeration is a must unless you have a big pond with constant inflow. Preferable water temp for the fish is between 20-28C.  Chlorine, Nitrite and ammonia are enemies of the fish.

2) Do not feed too much. Kingyo does not stop eating.

3) Put  Kingyo into salt water with 0.5% (5g/1Liter=kilo) for about a week. This kills parasite and/or bad bacteria of the fish. Be careful 0.7-0.9% salt water kills goldfish. Use natural salt only.  

Generally speaking goldfish is much more sensitive than Koi.


1.  "This is to lower Nitrous acid and ammonia in the water."
There is no real problem with Nitrous acid in fish ponds,     In  a good established natural pond, there is also no ammonia and no nitrite accumulation, as the pond's bacteria quickly break them down.    In older ponds without enough green plants, Nitrate buildup & Phosphate buildup can be a problem.   So,  if you accidentally killed off all your nitrifying bacteria by having chlorinated water,   then Nitritie & Ammonia do appear (and can be tested for with standard aquarium test kits), and Nitrite & Ammonia spikes  do kill fish ... just as you (Mainecoons) described.   If you have the chlorine levels you described,  then you likely killed off all the bacteria & facultative anaerobes that convert the fish's urine (urea nitrogen) to mostly-harmless Nitrate.

Test for Nitrite & Ammonia -  before you add fish,   and again later, every day after you add fish.   If the Nitrite & Ammonia levels spike up when adding fish, then you need to change 1/2 to 1/3 of the water to lower the Ammonia and Nitrate down to safe levels.  Also be careful with the amount of food you are feeding, as they should eat all the food within 3 - 5 minutes ~  otherwise the rotting excess food causes it's own water chemistry problem.

If your bacterial base that breaks down food waste & fish are still strong (doubtful with the chlorine levels you describe),   then you might have a problem with high Nitrates and possibly high Phosphates.  Test your water for these,  especially if Nitrite & Ammonia levels are extremely low.  Nitrate is removed by changing 1/3 to 1/2 the water ~ or by growing sufficient plants.  Phosphate can also be removed by 1/3-1/2 water changes - or by growing sufficient plants.

I've only maintained ponds for 7 years when running an aquarium & pond maintenance business,  and found when trying to operate a natural pond:  It is critical to    balance the number of fish ...  with the amount of feeding ... with the amount of plants ... with the size of the pond....  and controlling pH   (which can fall due to acid rain or algae blooms & die offs => eutrophication)

Fortunately,  this is all Aquaculture 99 level stuff,  and your water chemistry can be easily monitored going forward using standard Aquarium chemical test kits ~Ammonia & Nitrite only at the beginning or during crises~   pH regularly,   Nitrate  & Phosphate ~ weekly or monhtly ~ once the pond is established.

All of that still leaves unanswered the question of how you got high chlorine levels in your pond...   Some odd runoff ?

Maybe a gardener or mozo mistakenly add powdered or granular chlorine to the pond instead of the pool ?

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