# When do you replace the UV sterilizer light bulb?



## Olskule (Jan 28, 2010)

SpaceLord said:


> When do you replace the UV sterilizer light bulb?
> 
> I heard that even if the bulb has not burned out yet, it will lose its effectiveness in like 6 months.
> 
> ...


SpaceLord, yes, the effective full-power life of an UV fluorescent bulb is about six months, at which point it's only putting out about half of its rated UV light, so if you want the sterilizer to work at full strength after that, you should replace the bulb. However, one trick in using UV sterilizers is to start out with one that is twice the size that is recommended for your purpose, so that when the bulb is 50% weaker six months down the road, you still have the UV strength you need for your setup and don't need to buy a new bulb. I'm not sure how quickly the bulb loses strength after the six month/50% threshold; the rate of loss may slow down after that, but even if it drops another 50% in six months, you still got twice the life from an expensive bulb, and the (marginal) initial extra cost of the larger unit and subsequent replacement bulbs is more than made up by the savings of only having to replace the bulb half as often for the life of the unit. Incidentally, there is no harm in sterilizing with twice the UV you need initially, just keep in mind that all biologicals, even beneficial bacteria, will (theoretically) be killed in the water that passes through the sterilizer unit, so make sure to keep a steady supply of living bacteria in your filter and that the sterilizer unit is downstream of the filter.

Olskule


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## SpaceLord (Feb 29, 2016)

Olskule said:


> SpaceLord, yes, the effective full-power life of an UV fluorescent bulb is about six months, at which point it's only putting out about half of its rated UV light, so if you want the sterilizer to work at full strength after that, you should replace the bulb. However, one trick in using UV sterilizers is to start out with one that is twice the size that is recommended for your purpose, so that when the bulb is 50% weaker six months down the road, you still have the UV strength you need for your setup and don't need to buy a new bulb. I'm not sure how quickly the bulb loses strength after the six month/50% threshold; the rate of loss may slow down after that, but even if it drops another 50% in six months, you still got twice the life from an expensive bulb, and the (marginal) initial extra cost of the larger unit and subsequent replacement bulbs is more than made up by the savings of only having to replace the bulb half as often for the life of the unit. Incidentally, there is no harm in sterilizing with twice the UV you need initially, just keep in mind that all biologicals, even beneficial bacteria, will (theoretically) be killed in the water that passes through the sterilizer unit, so make sure to keep a steady supply of living bacteria in your filter and that the sterilizer unit is downstream of the filter.
> 
> Olskule


Perhaps that explains why I had so many fish die when I initially setup my aquarium. The UV sterilizer light was the first stage of the filtration and the biological media was the last stage. The UV sterilizer was probably keeping the beneficial bacteria from getting established leading to ammonia spikes. 

I have one of those Sun-sun canister filters and the UV sterilizer is in the channel that the intake siphon goes into. I have no ability to change where it goes. Also, I believe the protective cover is design to fit that size bulb unless you know of a larger one they make? 

Another idea I was considering is since I have an overstocked tank but only a canister filter rated for my exact aquarium size 75 gallons as well as the fact that the larger filters require like 3 times the energy to double the out. 

I was considering using 2 X 75 gallon(265 GPH) canister filters. 

That way I will be using 36 watts to filter 530 GPH and and having water pass slower by the UV sterilizing light maximizing contact time vs a single 525 watt canister filter which using 55 watts. 19 Watts power savings 24X7X365 probably adds up over the years. ( I am not a hippie, just want to save money so I can spend it on better tech, plants and fish for my aquarium) 

Anyway, if I deploy my second canister filter with a new bulb, it will be 100% while my existing bulb is lower than 50% effective. 

Perhaps between the 2 bulbs, I will always have a decent amount of sterilizing power for pathogens in the water hopefully enough to keep the fish healthy. 

Will the UV light always have some effectiveness as long as it has light until it burns out completely? 

What do you think of my 2 X 265 GPH canister filter solution using 2 UV sterilizers with always with 1 new and 1 very old bulb? 

Also, can you send me a link or let me know if these are capable of using this larger bulbs you talk about? 



I would love to hear more about this idea of using a double size bulb but I don't know how to go about installing one in this canister filter. 

See how there is like a protective glass test tube looking thing that only fits that one size bulb? 












Thanks.


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## Kubla (Jan 5, 2014)

The protective tube for a UV light is typically made of quartz (they can be a little pricey). With the UV light I use in my pond manufacturers say to change the bulb once a year. It is a larger bulb at 40 watts, not sure if that makes a difference or not. Some of the bulb manufacturers claim a longer life and recommend changing every 2 years.
I don't think you can change to a larger bulb. Besides the quarts sleeve being wrong, your ballast probably wont work.


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## Maryland Guppy (Dec 6, 2014)

High end UV lamps last about 8000 hours.
Glass is not used, quartz sleeves are used in UV applications to allow light penetration (UVC) at a maximum.
Call 8000 hours 1 year and I bet cheap lamps are only good for 6-8 months.

A tap off of a canister discharge is most likely the best option.
Recommend flow control to a UV light and low flow.
40-50 GPH should kill all single cell organisms and curb some algae and green water.


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## Lonestarbandit (Feb 7, 2013)

It is recommended to change the bulb every 6 months though I assume that is if it is run constantly otherwise clearly that interval would be extended.


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## Olskule (Jan 28, 2010)

When I mentioned buying twice the UV sterilizer size recommended for your application, I was referring to the whole unit, since the unit is designed to use a bulb of a specific size and wattage. I didn't realize that your UV was built into your canister filter, but I would consider the fact that it is located on the input side of the filter to be a design flaw, for the reason I stated previously, but there is nothing you can do about it now except be aware of the drawback and operate accordingly in the future. And yes, that probably was the reason you had a problem getting your nitrogen cycle going when you started out; most of the beneficial bacteria was being killed before it could get to the filter medium and establish itself, so the only nitrification taking place was happening on the surfaces inside the tank, itself.

Also, yes, using two filters at a slower rate per filter would be better IF the flow rate is reduced to below the filter's maximum capacity, because the built in UV lamp is matched to the maximum flow of the filter, and reducing the flow would increase the exposure time within the UV chamber. However, alternating the replacement of UV bulbs on two smaller filters which are both operating at maximum flow would be pointless because you would be buying a new bulb every six months anyway and, really, how many times can you kill the same organisms in the same water? Even paying for the UV in the second filter would be a waste of money. Personally, I prefer to run separate components so things are more tweakable, as mentioned above, by tapping a line from your filter output and running a UV unit at a slower flow rate for more thorough sterilization of the water that does pass through it. (Eventually, all the water will pass through it several times a day, if only a smaller amount at a time.)

Olskule


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