I have 4k litre pond (2m x 3m x 0.7m) with 8 8"-12" koi plus around half a dozen smaller goldfish/shubunkins, it's in full sun. It has 10kl/h water pump with matching pressure filter (UV no longer working), 10l/min air pump. The pond is mature, 10yrs+, fish seem happy and healthy but I've never managed to clear the green algae. I've tried various treatments, they give temporary improvement but it's never great and within a week or two it's pea soup again. There is a willow tree nearby so a lot of small leaves end up in the pond.


This Winter I'm due to replace the deck around the pond with patio so I need to get any new plumping/filtration in place; it seems a good time to review my setup and have another go at clearing the water.


I'm pretty clueless, so after a bit of independant advice.

  1. Clearly, (sorry!) I need UV but how much? I've found an article that suggests minimum of 16w, presuambly more is better?
  2. Also probably need a better filter, ideally low maintenance. Current pressure filter is under my decking, it regularly gets clogged with algae and removing it to clear requires a lot of effort. I'm looking at the likes of Eazypod, looks like easier maintenance but will need to be above ground. I Like the look of the "Complete" with built in UV but only has 18w UV, presumably I'd need a second UV? Eazypod are quite expensive, are they significantly better than other gravity/pressure filters?
  3. If I have a separate UV, should this just be inline on filter input/output?
  4. Would I benefit from a retrofit bottom drain/air diffuser, e.g Aqua-Jet?
  5. Do I also need a Skimmer or would bottom drain suffice, and if I have a skimmer does this need it's own pump?
  6. With the right setup, should I still need to treat the pond to keep it clear, if so how often?