Green pea-soup water is caused by free-floating algae, and a correctly sized UV clarifier is the simplest way to clear it and keep it clear all year. The right size depends on your pond volume, your pump flow and how many koi you keep.
How a UV clarifier works
Pond water is pumped past a UVC lamp sealed inside a quartz sleeve. The ultraviolet light damages the single-celled algae that turn water green, so they clump together and are caught by your filter instead of multiplying. It has no effect on your koi or plants, because only the water passing through the unit is treated.
Choose the size from your pond volume
UltraZap rates its pond UVs by pond capacity and maximum flow:
| UltraZap pond UV | Pond capacity | Max flow |
|---|---|---|
| 8 W | 6 000 L | 40 L/min (2 400 L/h) |
| 15 W | 15 000 L | 60 L/min (3 600 L/h) |
| 30 W | 30 000 L | 140 L/min (8 400 L/h) |
| 55 W | 50 000 L | 300 L/min (18 000 L/h) |
Find the size for your pond in the UltraZap Pond UV Clarifier range, or let the pond calculator choose it for you.
Three rules that make a UV work
- Size up for heavy stocking. Lots of koi and heavy feeding mean more nutrients and more algae, so choose the next size up.
- Respect the maximum flow. If water rushes through too fast it does not get enough exposure. On bigger systems, split the flow or run several UVs side by side.
- Put it after the filter. Clean water lets the light reach further, so the UV goes after mechanical filtration.
Clarifier or sterilizer?
A pond UV clears green water. A Professional UV sterilizer gives a stronger dose that also kills bacteria and parasites, which is why it is used on quarantine and hospital tanks and on marine systems. For large ponds and water treatment there is also a stainless steel UV with an internal quartz sleeve.
Keep it working
- Replace the lamp every year, ideally before spring. UVC lamps lose strength long before they stop glowing. Replacement UVC lamps
- Clean the quartz sleeve when you change the lamp; a film on the glass blocks the light. Replace it if it is cracked or permanently cloudy. Quartz sleeves
- UltraZap spares are made in South Africa and readily available, so a UV can be kept running for years.
Still green?
If the water stays green with a correctly sized UV, the cause is usually too much flow, an old lamp, or not enough filtration. Send us a photo and your set-up on WhatsApp (074 404 4539) and we will help.