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UV sterilizer and algae

MichaelJ

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Joined
9 Feb 2021
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1,187
Location
Minnesota, USA
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

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Joined
4 Mar 2021
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577
Location
Singapore
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. :)
 

MichaelJ

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Joined
9 Feb 2021
Messages
1,187
Location
Minnesota, USA
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

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21 Jan 2015
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Bracknell
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
 

MichaelJ

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9 Feb 2021
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1,187
Location
Minnesota, USA
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
 

erwin123

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Joined
4 Mar 2021
Messages
577
Location
Singapore
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.
 

MichaelJ

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Joined
9 Feb 2021
Messages
1,187
Location
Minnesota, USA
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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