Koi Pond Filter Systems: Bottom Drains, Drum Filters, Bio Media and UV

Koi are big, heavy feeders, and a koi pond has a very different waste problem from an ornamental pond. A filter system has to remove solids, convert toxic ammonia and keep the water clear, around the clock, in the heat of the UAE. This is how the parts fit together.

The stages, in order

1. Bottom drain

Waste settles at the lowest point of the pond. A bottom drain takes it away before it can decompose, and sends it to the filter by gravity or pump. It is the first and most important part to build in, because it cannot be added later without breaking the pond.

2. Mechanical filtration

Solids must come out before they dissolve. A settlement chamber, brush or screen is the usual route, and a drum filter is the more advanced one. A drum filter uses a fine rotating screen that removes particles automatically and keeps the biological stage cleaner.

3. Biological filtration

Beneficial bacteria on a large surface of media convert ammonia into nitrite and then nitrate. The media needs oxygen and constant flow. In warm water the bacteria work faster, but the fish produce more waste too, so the biological stage must be generously sized.

4. UV clarification

A UV unit treats free-floating algae that turn the water green. It does not replace the filter, but it is a useful part of the system.

Sizing

The correct size comes from the pond volume and the weight of fish you expect them to reach, not from the number of fish you buy on day one. Pump flow, the biological surface and the capacity of the solids stage all follow from that. Oversizing slightly is cheap protection; under-sizing is the commonest reason koi ponds go green.

Heat

Warm water carries less oxygen and increases fish metabolism. In a Dubai summer the system has to deliver oxygen through aeration and circulation, and some ponds need a chiller. Depth and shade lower the load first. Our summer koi pond maintenance guide explains what to do through the hottest months.

Where the filter goes

The plant room should be close to the pond, ventilated, drained and easy to reach. A system that is hard to service gets neglected. We design the room with the pond, not after it.

Maintenance in short

• Clean the mechanical stage as often as the system needs, not on a fixed date.
• Do not wash biological media in tap water; rinse it in pond water.
• Replace the UV lamp on the manufacturer’s schedule.
• Test the water regularly and act on trends, not alarms.

FAQ

Why does my koi pond keep turning green?

Usually too many nutrients for the filter, too much sun, or a filter that is too small. A UV unit helps but does not fix the cause.

Can an old pond be fitted with better filtration?

Often, although a missing bottom drain is hard to correct. We assess the pond first.

Our koi ponds start from AED 25,000, with filtration designed as part of the pond. See what drives koi pond cost or talk to us about your pond.

Further reading: The nitrogen cycle (Wikipedia)