Can You Have Too Much UV in a Pond?


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Your pond water is murky due to floating algae, then an ultraviolet (UV) filter is your best choice to clear it out. You’ll need to ensure you have enough UV to kill the algae and restore water clarity, but how much is enough and can you have too much?

You can’t have too much UV in a pond because the UV device only affects algae cells that go through the unit. So plants and anything else not suspended in the water are not harmed. However, it’s possible to have a device that’s too small for the job but you can’t have too much UV.

In this article, we’ll explain in detail how UV filters work to clear water in a pond, where to place the device, and how much UV light one needs for their pond. Stay tuned to the end, where we’ll also talk about the maintenance of the UV gadget.

How Does a UV Filter Work in a Pond?

A pond’s ecosystem needs to be cared for to maintain balance and ensure a healthy environment for the plants and animals (fish) living there. This includes keeping the water clean, clear, well-aerated, and free from toxins. 

This is why UV filters are one of the key devices used in ponds and water gardens. They are used to maintain the clarity of water; they achieve only if the turbidity is due to a floating algae build-up. 

So how exactly does the UV filter work?

  • Firstly, we need to point out that, though known as a UV ‘filter,’ technically, this device isn’t a filter because it does not physically remove clumped algae from the water. Instead, the UV light works by killing living organisms, especially bacteria, and floating single-celled algae.
  • Water is pumped through the UV filter, then bacteria and algae that pass in front of the UV light are destroyed. The high level of ultraviolet light destroys the DNA of the algae and kills them. The dead algae clump together, making it easy to remove them from the water through the use of mechanical or biological filters.

Check out this video showing the difference a UV filter can make on your pond: 

Does UV Light Kill Beneficial Bacteria?

As I’ve mentioned, the UV filter destroys organisms in the water that passes in front of the UV lamp. This means that the ultraviolet rays destroy both useful and harmful bacteria. As long as they float in the water and hence pass through the UV filter.

This concept often results in a lot of concern about whether a UV filter can kill all beneficial bacteria and sterilize a pond. The answer to that is a resounding ‘No.’ 

Pond UV light cannot destroy all the useful bacteria because most of them usually reside at the bottom and the sides of the pond or in the filter pads. This means that only a few beneficial bacteria will go through the UV light and get destroyed.

Placement of UV Pond Lights

The position of the UV lights is important in ensuring the device does its work efficiently. 

Here are a few things to remember:

  • If it’s a submersible model, e.g., the Jebao UFP-2000 Submersible Pond UV Filter that can be found on Amazon, should be placed underwater. You then need to attach a weight to this type of UV device if you don’t want it floating around in the pond. But most UV filters are out-of-pond models and so are placed outside the pond. 
  • Another essential thing to note is the UV light’s position with the filter (either the biological or mechanical filter). The UV light ought to be placed inline with the pump and the filter. This order means the pond water is pumped, passes through the UV clarifier/ sterilizer, then the filter removes the dead algae.
  • Be cautious about the position of the intake and output hose. The UV light will be fed by the pump’s intake tube. This needs to be placed as far as possible from the tubing that returns water to the pond.
  • If the inlet and outlet pipes are too close to each other or the inlet close to the fountain or waterfall, you will only be pumping relatively clean water through the UV filter. This won’t be efficient since some algae, and other pollutants in the water will hardly go through the filter. 

How Much UV Is Enough?

This is one of the challenging questions among pond-owners. The simple answer is that, whenever you want to buy a UV filter, look at the manufacturer’s chart because the specifics are based on the models themselves. 

These charts show the ideal wattage for different sizes of ponds. But whenever you’re in doubt, it’s better to go for a bigger size since it will get the job done and not cause any adverse effects. That’s better than getting a device that’s too small, then end up in a situation where you can’t seem to get rid of the algae in your pond. 

How to Size a UV Filter

There are two kinds of pond UV filters: clarifiers and sterilizers. A good example of the clarifiers is the TetraPond GreenFree UV Clarifier (link to Amazon). It’s easy to conceal, durable, and can typically remove massive algae within five days. The Jebao 36W Fish Pond UV Sterilizer from Amazon is one efficient sterilizer that can permanently eliminate algae bloom so you don’t need to worry about green pond water again.

These devices have different levels of effectiveness, which are based on various factors. For example, if the wattage is equal, a clarifier will not be as effective as a sterilizer. 

So why is this important? It’s necessary to know which device will treat your pond water and keep it crystal clear. This will help you decide which type of UV device to purchase.

Calculate Pond Size in Gallons

Your pond size will help you figure out how many gallons of water you need to pump per hour. This will then determine the best-sized UV filter for your pond.

To determine your pond size in gallons:

  1. Measure the length, width, and depth of your pond in feet. 
  2. Multiply these figures to get the size of the pond in cubic feet.
  3. For every cubic foot, there are 7.48 gallons of water. So next, multiply your pond’s volume by 7.48.

Determine the Flow Rate

Flow rate refers to the number of times you want to pump the entire contents of your pond. This is an essential factor to consider, and there are various elements to help you decide on the rate. 

For example:

  • If your pond does have fish or not
  • The quantity of fish
  • The debris that falls into the pond
  • The prevailing climate

In general, if you have fish in your pond, it’s advisable to pump the entire pond water at least once every hour.

Having these details, i.e., the pond size and flow rate, can now correctly identify the UV filter that matches these specs.

Maintenance of Pond UV Filter

UV filters are relatively maintenance-free devices. There are just two key things to keep in mind: cleaning and lamp replacement.

As pond water passes over the UV filter sleeve, dirt will be deposited there over time. Therefore, you will need to clean this every so often to ensure enough UV light is getting into the water.

As for the replacement, this should be done when you notice that the UV bulb is no longer working. As a standard, most manufacturers advise on replacing the lamp after one year of use.

Here’s a short video demonstrating how to test your UV bulbs: 

Conclusion

UV filters are essential devices for treating ponds and removing floating algae. This device only affects organisms that pass in front of the UV lamp.

As discussed in this article, the ultraviolet rays kill both beneficial and harmful bacteria plus the suspended algae. But the good thing is that beneficial bacteria are rarely suspended in water. Most are located at the bottom or sides of the pond. So there is no way the UV light will sterilize your pond water.

With that in mind, it’s safe to say that you cannot have too much UV in a pond.

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Lars

I am always happy to share all my knowledge about how to keep your garden in good condition and make it special.

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