UV Sterilizer for Fish Tank – Know About It

A UV sterilizer might not be on the list of primarily essential items for a fish tank like an aquarium filter or heater. Still, it is a useful tool to maintain a healthy aquarium. The function of the UV sterilizer is somewhat prophylactic for a fish tank.

The UV sterilizer prevents spreading diseases inside an aquarium by killing germs. It also kills algae and controls algal bloom.

If you have a cloudy water problem in your fish tank, a UV sterilizer can remedy it. You can use it also as a preventive safeguard. In this article, I’ll talk about UV sterilizers and how they work for a fish tank.

What is a UV sterilizer for fish tanks?

A UV sterilizer emits ultra violate ray that kills harmful organisms present in the aquarium water. Thus UV sterilizers prevent the parasitic and bacterial infections to which your fish tank is always susceptible. It also controls algae growth.

A UV sterilizer controls spreading diseases from one fish, coral, or invertebrate to another. However, it does not treat sick fish or others because UV sterilizer can kill microorganisms only in the water without any pathogens attached to fish.

How does a UV sterilizer work?

The working principle of the UV sterilizer is a bit technical. Now I will talk about the science behind it in short. If my definition becomes hard to follow, just ignore it. Knowing technical details is not necessary to use it.

UV sterilizers use germicidal fluorescent light that produces UV rays with a wavelength of approximately 254 nanometers. This light is capable of destroying the DNA (genetic material) of single-cell organisms like pathogens. Thus it prevents the multiplication of them.

UV sterilizers come with tubes that emit UV light, and water flows through them. Some sterilizers have their own water flowing mechanism, while others are installed at an external filter’s output. Purified water, after filtration, enters the UV sterilizer and gets rid of unwanted germs in it.

Should I use a UV sterilizer in the aquarium?

As I said before, a UV sterilizer may not be the first liner among essential aquarium items. Still, it has some great benefits to use. Here I mention three reasons why you can use a UV sterilizer in your aquarium:

should i use a uv sterilizer in aquarium

1) Prevents spreading infections

Using a UV sterilizer in the aquarium is somewhat beneficial. In many ways, germs can enter the aquarium. Once an aquarium member gets infected, it can be spread to others and cause a disaster.

A UV sterilizer kills the pathogens present in the water before they infect your fish, coral, or invertebrates. Thus it reduces the risk of disease spreading.

Especially in a heavily stocked tank with a large number of fish or in a reef tank having too many live rocks and corals, UV sterilizers come to be essential. Because in such tanks, an infected member is challenging to identify and isolate. Hence the chance of spreading infection is high.

2) Controls algal bloom

A UV sterilizer is useful to control algal bloom. Many aquarists face algae problems, and sometimes it becomes uncontrollable. Excess algae cause oxygen deficiency in the water, and fish can suffocate.

Algae is harmful to live aquarium plants in a planted tank. So killing algae is also beneficial, and a UV sterilizer is quite useful to do this job.

3) An alternative to the quarantine tank

Having a UV sterilizer is very useful when you add new fish to an established aquarium. Adding newly bought fish directly to the main display tank is not the best-recommended practice as new fish can carry pathogens from pet stores.

I suggest quarantining new fish in a quarantine tank before putting them in your main aquarium. But the fact is 98% of aquarists don’t use a quarantine tank. And so, a UV sterilizer is an alternative that can prevent spreading diseases from new fish to other members of your aquarium.

4) Effective safeguard at a reasonable price

A UV sterilizer is not such a pricy item and not really unaffordable. But for smaller aquariums, less than 20-gallon, the cost might be impractical.

Some people say it is like an insurance policy for your fish tank. It eliminates many risks associated with fish keeping. Thus this safeguard can reduce your stress and tension, making the hobby more enjoyable.

The downside of using a UV sterilizer in your fish tank

There are some limitations to using UV sterilizers in aquariums. Here I am giving the significant points.

1) Kills good bacteria in the water

The primary side effect of a UV sterilizer is it kills all bacteria regardless of good or bad. So, it will kill beneficial bacteria that flow through the water. But it would not be that significantly negative, as beneficial bacteria colonize in the substrate or filter media.

It is not the best practice to use a UV sterilizer during cycling a tank. It can slow down the multiplication of beneficial bacteria, and so your cycling process will be delayed.

2) Denatures medications

If you are dosing medicines to the tank, it is better to keep off the UV unit as many medications can be altered and ineffective in the presence of UV light.

3) Impractical for small and large tanks

A UV sterilizer unit’s cost is not economical when using it in a small tank below 20-gallon. Also, in small tanks, the UV unit can raise the water temperature. Sometimes a chiller is required to maintain the water temperature.

A UV sterilizer cannot function well in larger aquariums because it requires a low flow rate, impractical in large tanks.

4) Not effective for all types of microorganism

A UV sterilizer is not cent percent effective dwelling aginst all types of microorganism. For example, it is not effective against string algae and some particular kinds of bacteria.

A UV sterilizer kills only microorganisms that are free-swimming in the water. Therefore, it cannot treat a sick fish by killing the pathogens attached to its body. At the same time, they are incapable of destroying germs hiding inside the substrate.

How long to run a UV sterilizer in an aquarium?

In an established tank, the ideal practice is to switch on and keep running the UV sterilizer non-stop 24 hours a day. Thus you can get the best output from a sterilizer.

Besides keeping it 24 hours running, it is essential to ensure UV bulbs’ integrity and efficiency. Therefore, it is advisable to replace the bulbs after 6 to 12 months of putting them in service. The manufacturer can suggest to you the more exact frequency for replacement.

Where to put UV light in an aquarium?

Some aquarium UV sterilizers have their own flow arrangements. That means it can suck the water inside the tube by its own motor. You can put them anywhere suitable in the aquarium.

But the most common UV sterilizers don’t come with their own flow mechanism, and you have to install them to win an external canister filter. The ideal practice is to connect the sterilizer with the filter’s outflow so that filtrated water enters for sterilization. 

If you allow unfiltered water inside the UV sterilizer, it promotes quartz sleeve fouling, limiting UV bulbs’ effectiveness. So, if you have no option to install the UV sterilizer after the filter, ensure adequate pre-filtration by any alternative way. 

How long does it take for UV light to kill algae?

A properly sized UV sterilizer is vital for better efficiency. The correct placement of the unit is another important consideration. If you connect an adequately sized UV sterilizer after the filter, it should not take more than 3 – 5 days to make water clear.

From other user’s experiences, I came to know that if you place a UV sterilizer before the filter, it may take a longer time of 7- 10 days to clear the aquarium water’s cloudiness.

If you experience green water in your aquarium, a UV sterilizer can help eliminate it within 4-5 days. Within a day after installing it, you’ll observe the water becoming greyish green and transparent in the next few days.

Factors affecting a UV sterilizer’s efficiency

Several factors can determine how efficiently a UV sterilizer will work in a fish tank. Among all aspects, I’ll discuss the most significant three:

efficiency of UV sterilizer in the aquarium

1) The capacity of the sterilization unit

The UV sterilizer’s capacity depends on the power of UV bulbs and the UV light’s penetrability. Bulbs should have adequate wattage, as bulbs with higher wattage produce more UV lights.

The ability of a UV sterilizer to kill microorganisms depends on the penetrability of UV lights. If light cannot penetrate the water sufficiently, the efficiency will be less. UV lights can penetrate clear water more quickly, so installing the UV sterilizer after a filter is recommended.

Besides turbidity, salinity in reef tanks also affects the efficiency of a UV sterilizer. As salinity increases, the penetrability of UV light decreases. So, saltwater and reef tanks require more powerful UV sterilizers than freshwater aquariums.

2) The contact time

The longer the water remains exposed to the radiation, the more germs will be destroyed. So the contact time also refers to the dwell time. So if water passes quickly through the UV tubes, it will get less contact time.

You can increase this retention time by lowering the flow rate or getting longer UV tubes.

The total percentage of aquarium water that comes in contact with UV lights determines the overall sterilization efficiency. It is impossible to ensure all the water is passing through the tubes, but the turnover time (the required time to pass all the aquarium water through the UV sterilizer) is a measurement to consider for this.

3) Types of organisms present in the aquarium

Typically a standard UV sterilizer can kill common bacteria, fungus, and algae. But if larger organisms like protozoa are present in your aquarium water, the efficiency will be less as higher UV dosing is required for killing them.

Additionally, some bacteria are proven UV resistant relatively. If this kind of organism enters the aquarium, the efficiency of sterilization comes down.

Final Words

There is some risk associated with using UV sterilizers, including the health hazards of the users. A UV sterilizer kills microorganisms by irradiating them. And exposure to these sorts of radiation is not good for human health.

Though it is not so significant still if you decide to use UV sterilizers, be sure you know well about the side effects of using them.

If you use a UV sterilizer for the fish tank, get a quality one. That will help to maintain a healthy water condition. But remember that a UV sterilizer is not an alternative to good mechanical or biological filtration.

Finally, I would love to hear about your experience with UV sterilizers. Is it useful in your opinion? Please don’t hesitate to drop a comment below.

Sujit Modak

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