Milky or Cloudy Pond Water

Around this time of year (autumn in the UK) people often complain of the water in their pond turning cloudy or milky. You may get changes in water quality throughout the year, but it can usually happen when summer changes to autumn. First, its the time of year when the temperature is dropping down and the cycle in your pond is going to slow down and change.

I experienced some milky water for a couple of different reasons, but if you are experiencing this problem consider the following points:-

1. You have given your filter setup a really good shake-up and cleanout. This can result in some fine particles going into the pond. This is cloudiness due to sediment and particles which have become waterborne.
2. Having been disturbed by the filter cleanup, some of the good bacteria in the filter can die off and weaken its process on cleaning the pond water and keeping it clear. Usually this can be remedied by adding some more bacteria culture, although at this late time of year the bacterial processes will be slowing down and dieing off themselves anyway.
   
3. Green water is associated with too much algae - an algal bloom, and Brown water is associated with too much sediment or particles. Milky water is usually due to algal bloom "die-offs", e.g. temperature too low for the algae to live so it dies. So with autumn upon us your pond has now cooled down sufficiently to cause a die off.
4. Have you changed your food? Around this time of year when the temperature changes and goes below 10 degrees Celsius the fish cannot digest the usual summer food pellets. You should change to a wheatgerm based winter feed and slow feeding right down as the winter months draw in, until at some point the fish simply will not want to eat any more food. Continueing to use the summer food isputting too much nutrient into the water which may also exacerbate the milky water problem.
5. Another reason for milky or cloudy pond water is if you have had excessive rain. Again, autumn brings changes, more rainfall being one of them. This may have caused a run-off ofdirt, clay or even chemicals into the pond from your garden and so could account for the change in water quality.
6. You will also find at this time of year that fish change their feeding habits from eating the large summer food pellets as mentioned in point 4 above (so they leave it uneaten and it just rots and causes milky water). When they have slowed right down on their eating, as mentioned you should change to a winter food based on wheatgerm. But also now the fish tend to grub around at the bottom of the pond, looking for small, fine particles or grubs, little critters etc (I guess they know best what to eat to prepare for winter). Anyway - all that grubbing around, especially from the larger fish, does a lot of stirring up of the muck at the bottom, and if you have a venturi in the pond this will mix up the sediment in the pond, giving the water a cloudy appearance.
   

It will be best to concentrate on likely reasons for the milky or cloudy water being the feeding and the temperature change as the problem, rather than your filter, provided you have been continueing a normal routine for cleaning the filter. If you do something drastic to clean the filter too much then you will probably kill off the bacteria, and at this time of year they will have a hard time at recovering. So perhaps leave the filter alone (unless it looks incredibly dirty), because you want the filter to continue cleaning up any algae bloom die-off. Normally I try to leave a major dis-assemble and cleaning of the filter until the water has become quite cold and all bacterial processes will have died off completely.

Hopefully this will help explain a number of possible causes for the condition.