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Small New Pond Problems

Dear Ben,
I have got a little pond, only 5ft x 4ft, and 18in deep, I have six little koi (5in long) and eight little orfe (2in long maximum). My pond has a filter pump going through a UV clarifier and into a box filter, it is quite a new pond about two months old.

My problem is the water quality is not good, I have done numerous things to rectify it, and as I'm new to koi keeping I'm very keen to get it right.

The pH is 8.5 the ammonia is steady at 1.2mg the nitrite is 1.0mg and the nitrate is 50-100mg. I have turned off the UV to give the bacteria in the filter time to mature and have steadily added more bacteria to the filter to help the nitrite levels reduce, I may have over fed the fish a bit at first, but I have now reduced feeding down to next to nothing for the last week.

I have added some pond salt to help and have been adding Ammonia Away, this does reduce the level temporary but it rises again slowly. The pond is made of Railway sleepers with a pond liner inside and the fish seem happy enough. My neighbour who has koi says I'm worrying too much, but I know with my limited knowledge that the levels should not be this high. I have done a partial water change down to six inches from the bottom, are the bacteria being affected by the Ammonia Away, and salt, and water changes?

Never mind being addicted to koi, I'm now addicted to testing the water! Can you help as I would like to get the water right before it starts to affect my new little friends.

Welcome to the world of koi keeping - and the obligatory steep learning curve!

Your experiences are not uncommon amongst koi keepers as all of us have had to tread carefully through the first few months as our pond and filter matures to support a balanced, healthy stock of fish.

There are recommended ways of accomplishing a mature pond without encountering too many water quality problems, but from your description, it sounds as though you might have made a number of unfortunate errors that are only now starting to cause you some problems.

Your pond is experiencing classic New Filter Syndrome (NFS), which unfortunately is being compounded by the small volume of your pond and the relatively high stocking density.

As the trickle continues, the concentration of ammonia starts to rise until the pond's water quality is in danger of stressing your fish.

To confirm this, your tests show that you have unacceptably high ammonia and nitrite readings as a result of the under performing filter in relation to the demands that your fish are putting upon it.

This is because fish excrete ammonia because it is toxic.

So, by excreting it into the pond water, your whole pond environment inevitably turns toxic (unless it is broken down at the same rate by bacteria).

You've been adding salt which will reduce nitrite toxicity, but your best approach is to create a nitrite-free pond - especially as you'll be diluting your salt content every time you carry out a water change.

Once your filter has fully matured, you should not encounter any further water quality problems (assuming you do not overfeed or overstock your pond).

pond water fish ammonia filter nitrite "water quality" "water change" bacteria NFS mature experiencing "Filter Syndrome" unfortunate encounter click to read full article


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