# UV sterilizer and algae



## idris (13 Jan 2022)

Today an LFS recomended a UV filter for treating algae. I've not come across this suggestion before. I know it's not likely to be the whole solution, but is it legit?


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## Ria95 (13 Jan 2022)

UV is good to treat/ damage  algae and pathogens which are in the water column. For this reason it works great against green water but will be  limited against other algae types. It will also damage micronutrients chelation.


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## Wookii (13 Jan 2022)

idris said:


> but is it legit?



It's a legit way for your LFS to increase their sales and profits for sure!  Not a great deal of use beyond that on a planted tank.


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## erwin123 (13 Jan 2022)

I tried it once, not helpful at all for algae. may help with fish health  if you get a sufficiently powerful unit that can kill pathogens - eg: in an outbreak in a community tank, quarantine the sick fish, whip out the UV (high power/low flow rate is key) for the main tank to prevent spread of disease to healthy fish.


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## idris (13 Jan 2022)

That's what I thought. I guessed it could slow the spread of algae between plants, but I wasn't convinced it would do much else.


Wookii said:


> It's a legit way for your LFS to increase their sales and profits for sure!


Wash your mouth out!


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## arcturus (13 Jan 2022)

idris said:


> That's what I thought. I guessed it could slow the spread of algae between plants, but I wasn't convinced it would do much else.
> 
> Wash your mouth out!


There is a lot of snake oil in aquaristics. But UV filters are not in that group. UV filters are useful to remove pathogens from the water, and they do help with bacterial blooms, and with the removal of algae spores and other organisms that are suspended in the water column. They will not work if they are incorrectly set up, which is most often the case.

The water must be exposed to strong UV radiation for a certain amount of time for the organisms to be damaged or destroyed. Otherwise nothing happens. This means that the water must flow through the filter quite slowly. If you use a unit with UV light of ~10W or less (which you will find in the majority of entry level models), the water flow should not exceed say ~100 l/h.  If you get a unit with a UV light of 20-30W maybe you can raise the flow to 300-400 l/. However, UV filters are often connected directly to the output of canister filters sometimes generating a flow of +1000 l/h. A UV filter must be connected to a low-flow water circuit (either by building a canister filter bypass, or using a separate circuit with a low-flow pump). Otherwise the filter will not work due to incorrect installation.


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## jaypeecee (13 Jan 2022)

idris said:


> Today an LFS recomended a UV filter for treating algae. I've not come across this suggestion before. I know it's not likely to be the whole solution, but is it legit?


Hi @idris 

It can certainly kill off algae spores and Cyanobacteria _when suspended in the water column_. As water passes through the UV-C sterilizer carrying spores and filaments, the high energy UV-C damages the DNA of living matter that passes through it. That's all there is to it. In order for this to be effective, _dwell time_ is all-important. As the name suggests, 'dwell time' is the time that the bacteria and/or algae are exposed to the UV-C light. And this is determined by the physical dimensions of the sterilizer itself and the flow rate. The presence of particulate and dissolved organic matter (POM/DOM) in the water column absorbs UV-C (at 254nm) and can then reduce the effectiveness of UV-C sterilizers.

I have used a UV-C sterilizer to good effect in combatting Cyanobacteria.

JPC


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## hwscot (13 Jan 2022)

One that seems to be widely available and stresses the low flow rate is the 'Green Killing Machine', available with either a 9w or 24w UV tube. Anyone have experience of these?


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## MichaelJ (14 Jan 2022)

Hi @hwscot yes, I use the Green Killing Machine 9 W UV filter in both my tanks - I have it set on a timer to run for 4 hours a day in the evening. It kills algae spores and pathogens (below a certain size) that floats around in the water column. Beware that the UV light may interact with Iron chelates (essentially breaking down chelating agents) and render Iron less available to the plants, so try and dose micros outside the timeframe where the UV light is running. Yes, it zaps beneficial bacteria that lives in the water column as well, but the bacteria we rely on are mostly in the substrate and filter... Otherwise, I cant think of any downside to running a UV filter (if you can easily hide it somewhere).

Cheers,
Michael


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## jaypeecee (14 Jan 2022)

hwscot said:


> One that seems to be widely available and stresses the low flow rate is the 'Green Killing Machine', available with either a 9w or 24w UV tube. Anyone have experience of these?


Hi @hwscot 

I use the _Mini Green Killing Machine_. I can provide more information tomorrow if you wish but, now, I must take a break.

JPC


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## erwin123 (14 Jan 2022)

I presume those that are running UV in their tanks are doing so for overall fish health, rather than algae reduction?


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## hwscot (14 Jan 2022)

Thanks, guys,
To come clean .. I just bought one. As it happens, I set it up just yesterday.  The 9w. It's a tank that's only been running a few weeks and doesn't have a serious problem with algae, having passed quickly through a diatom stage, and the tank layout lets me hide it quite easily. I panicked a bit when I saw the thread and the degree of scepticism. It's reassuring to have some positives, and interesting to get the experience on running times.


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## hwscot (14 Jan 2022)

erwin123 said:


> I presume those that are running UV in their tanks are doing so for overall fish health, rather than algae reduction?


That was my purpose, yes. Though it can't harm to be inhibiting algae in the water column.


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## hwscot (14 Jan 2022)

MichaelJ said:


> (if you can easily hide it somewhere).
> 
> Cheers,
> Michael


I'm going to have to post a shot of the tank. I know i am. It's possibly the most anally-retentive design, if that's the word, that UKAPS has ever seen. Very rectilinear. But the UV steriliser is certainly well hidden.


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## arcturus (14 Jan 2022)

erwin123 said:


> I presume those that are running UV in their tanks are doing so for overall fish health, rather than algae reduction?


This is a very good question.

A suitable* UV unit will damage or destroy a variety of organisms suspended in the water column, including infusoria up to a given size, pathogens, as well as algae spores, including cyanobacteria as @jaypeecee mentioned above in this thread. An UV unit has no impact (at least no direct impact) on the organisms on the surfaces of the aquarium.
* a UV filter that generates sufficient UV radiation exposure given the input water flow, and has sufficient turnover rate given the total water volume.

But there are <studies> <investigating> the effect of UV radiation on some algae sp. using not only UV-C but also the higher wavelength <UV-A and and UV-B>. Studies routinely look at <the impact of UV on cyanobacteria sp.> since bacterial blooms are suspended in water.

I believe there is no evidence demonstrating that UV will not reduce the load of some of the several thousands of algae sp.. Given existing research and how UV is actually used in practice (e.g. in water treatment plants), it is most likely that UV will also reduce some algae sp. in a planted aquarium, but this needs to be demonstrated.


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## jaypeecee (14 Jan 2022)

hwscot said:


> I'm going to have to post a shot of the tank.


Hi @hwscot 

Yes, please!

JPC


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## jaypeecee (14 Jan 2022)

Hi Everyone,

One of the good things about a UV-C sterilizer is that it can be switched ON or OFF, as required. And this applies whether it is stand-alone or inline. In the case of the latter, it is important to choose a unit that doesn't significantly reduce water flow rate. If using tank medications, manufacturers may advise switching a UV-C sterilizer OFF.

JPC


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## erwin123 (14 Jan 2022)

UVC Sterilization | How Aquarium & Pond UV Sterilizers Work
					






					www.americanaquariumproducts.com
				




The website sells UV products, so obviously they are touting the benefits but when it comes to algae, this is what they have to say:


> BETTER is rather than spend more than is needed for an extra large or a couple of UVs just to battle some extra algae growth is to simply *establish* your marine aquarium with truly seasoned live rock and also *practice some patience.*
> Ditto a pond, allow for* maturing of the pond, *add a Veggie Filter, use some Pond Stability and Enzymes and save your money in UV Sterilizer "overkill".


Mature (stable) aquarium = best solution for algae problems?  (but ok, they want to sell you some magic water to help your tank mature faster...)


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## Oldguy (14 Jan 2022)

I use a 30 Watt unit on a time switch. Dwell time and turn over are critical to its effectiveness.


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## arcturus (14 Jan 2022)

erwin123 said:


> UVC Sterilization | How Aquarium & Pond UV Sterilizers Work
> 
> 
> 
> ...



In my comments above I am not defending the usage of UV products as some sort of magic solution to stabilize a tank or to remove algae. But UV products are often discredited as producing absolutely no effects, which is incorrect. UV products do have impact on algae and bacteria suspended in the water, and play a role in situations that require specific water treatments.

So let's not conflate the discussion about "do UV products have any impact on algae and bacteria" with the discussion about "should we use UV products in a planted tank as a primary means to stabilize it and control algae". These are two separate discussions.


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## MichaelJ (14 Jan 2022)

I totally agree with @arcturus   It's beyond reasonable doubt that UV light kills some (not all) bacteria and some (not all) algae spores that are suspended in the water column... Yes, the efficacy depends on a multitude of factors, including intensity of the UV light, exposure time (i.e. flow throughout the UV filter vs. UV strength etc.).  However, by no means should deploying a UV filter be thought of as a substitute for proper maintenance such as water changes, appropriate stocking level, filtration/flow etc. - it's just an extra guard rail that may offer some protection against certain pathogens and certain algae.

Cheers,
Michael


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## erwin123 (15 Jan 2022)

As recently as last year, I had an 11w UV unit connected to my canister filter (for reference, it was a new bulb as UV-C bulbs decrease in efficiency pretty rapidly, which is also why I went for an 11w over a 9w.. to give some 'buffer' as the UV-C bulb drops in effectiveness over time).  The UV unit was good for fish health in the sense that I basically had no fish health issues (hard to prove a 'negative') . Once I had a newly introduced fish with white spot but  I credit the UV unit for 'cleaning' the water column and none of my other fish got it.

However, in UKAPS, I read that flow is king so I removed the UV unit as an experiment. I'm sure that the UV was killing algae spores in the water column but it did not translate into a visible difference in my tank (I have been taking weekly photographs for my tank for reference).

This is just my experience which is just one data point, I look forward to hearing how UV has benefited others' planted aquariums. My UV unit is still in my storeroom ready to be deployed anytime its needed.


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## MichaelJ (16 Jan 2022)

erwin123 said:


> As recently as last year, I had an 11w UV unit connected to my canister filter (for reference, it was a new bulb as UV-C bulbs decrease in efficiency pretty rapidly, which is also why I went for an 11w over a 9w.. to give some 'buffer' as the UV-C bulb drops in effectiveness over time).  The UV unit was good for fish health in the sense that I basically had no fish health issues (hard to prove a 'negative') . Once I had a newly introduced fish with white spot but  I credit the UV unit for 'cleaning' the water column and none of my other fish got it.
> 
> However, in UKAPS, I read that flow is king so I removed the UV unit as an experiment. I'm sure that the UV was killing algae spores in the water column but it did not translate into a visible difference in my tank (I have been taking weekly photographs for my tank for reference).


Hi @erwin123  Yes, having the UV applied on a powerful canister filter (i.e. inline) is certainly not a good approach. The efficiency of the UV light is a pure function of wattage and exposure, so if the UV is applied on the canister inlet or outlet it will have to be a tremendously high wattage to have any effect due to the relatively high flow rate - and as you point out, flow is king so you do not want the UV application to interfere with your overall goal of flow/distribution.  That's why I use and recommend a dedicated UV filter such as the GMK of relatively low wattage (which also makes it much more affordable), but with relative high exposure due to the low flow throughout the filter.  As for longevity of the bulb that is more a function of burn hours, but you're right they do degrade quite rapidly and sometimes rather ungraciously. In my case running my GMK 9W (50 GPH) for 4 hours a day should give me enough to sanitize the water column at least one time over in my 150 Liter tanks and definitely make the bulb last for about a year (a replacement bulb is about 20 USD).

Cheers,
Michael


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## jaypeecee (16 Jan 2022)

jaypeecee said:


> The presence of particulate and dissolved organic matter (POM/DOM) in the water column absorbs UV-C (at 254nm) and can then reduce the effectiveness of UV-C sterilizers.


Hi Everyone,

And, for the above reason, I guess there may be a possibility that chelating compounds - EDTA, Ferrous Gluconate, FeDTPA - may also absorb UV-C. Needs some investigation, I suppose? It's never straightforward, is it? At least the UV-C sterilizer can be ON or OFF at the flick of a switch. Phew!

JPC


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## MichaelJ (16 Jan 2022)

jaypeecee said:


> Hi Everyone,
> 
> And, for the above reason, I guess there may be a possibility that chelating compounds - EDTA, Ferrous Gluconate, FeDTPA - may also absorb UV-C. Needs some investigation, I suppose?


Hi @jaypeecee  Yes, and thats why, with this uncertainty in mind, I try to dose all my traces a reasonably amount of hours before the sterilizer comes on. Personally, I haven't noticed any Fe or other deficiencies in my tanks regardless.

Cheers,
Michael


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## erwin123 (16 Jan 2022)

MichaelJ said:


> Hi @erwin123  Yes, having the UV applied on the canister (i.e. inline) is certainly not a good approach. The efficiency of the UV light is a pure function of wattage and exposure, so if the UV is applied on the canister inlet or outlet it will have to be a tremendously high wattage to have any effect due to the relatively high flow rate - and as you point out, flow is king so you do not want the UV application to interfere with your overall goal of flow/distribution.  That's why I use and recommend a dedicated UV filter such as the GMK of relatively low wattage (which also makes it much more affordable), but with relative high exposure due to the low flow throughout the filter.  As for longevity of the bulb that is more a function of burn hours, but you're right they do degrade quite rapidly and sometimes rather ungraciously. In my case running my GMK 9W (50 GPH) for 4 hours a day should give me enough to sanitize the water column at least one time over in my 150 Liter tanks and definitely make the bulb last for about a year (a replacement bulb is about 20 USD).
> 
> Cheers,
> Michael



It depends on which canister filter. I was running 2 canister filters and the slower one was a Eheim Classic 250 which is rated at 440l/hr (115gph). After packing it with media, I measured the flow at about 55gph (i.e half the published flowrate).  So an 11w UV was more than enough for 55gph flow. But you have brought up a good point about not running it 24 hours a day - I experimented with various timer settings and didn't see the need to run it 24/7 unless there was a sick fish or some other visible problem I suppose.


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## MichaelJ (16 Jan 2022)

erwin123 said:


> It depends on which canister filter. I was running 2 canister filters and the slower one was a Eheim Classic 250 which is rated at 440l/hr (115gph). After packing it with media, I measured the flow at about 55gph (i.e half the published flowrate).  So an 11w UV was more than enough for 55gph flow.


Yep, 11W @ 55 GPH that should be enough. Point is, as long as the UV application won't interfere with flow goals and have enough wattage for the flow, then it's all good. otherwise use a dedicated UV filter.

I edited my post to stress powerful canister filter   ... I alway think of canisters as powerful, but of course, that is all relative... 

Cheers,
Michael


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## hwscot (19 Jan 2022)

jaypeecee said:


> Hi @hwscot
> 
> Yes, please!
> 
> JPC


I have now done this (Journals) and am a bit nervous!


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