# old light bulbs cause algae?



## crypto (Apr 12, 2012)

I have read this more than once on this forum, and I'm paraphrasing: "Old bulbs cause algae." To me, this seems like a myth, but I would appreciate feedback from anyone with more experience on this one.


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## herns (May 6, 2008)

crypto said:


> I have read this more than once on this forum, and I'm paraphrasing: "Old bulbs cause algae." To me, this seems like a myth, but I would appreciate feedback from anyone with more experience on this one.


My bulbs are closed to 2 year old or mayber over 2 yrs old and i dont have algae. But, I have read a book that says old bulbs caused algae.


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## DarkCobra (Jun 22, 2004)

It's simple, really. The amount of light produced by a bulb drops over time.

In particular, the amount of red light drops more quickly than other colors (spectrum shift). The human eye is most sensitive to green, and doesn't detect loss of red well. It's also a poor judge of absolute intensity overall, because it has a logarithmic response. If a light appears half as bright to the eye, it's only emitting a _quarter_ as much energy.

Plants gather this energy, and require both red and blue light. What may appear as only a slight dimming of a bulb over time to us, is a much greater reduction of light to plants; especially red light. Once usable light drops too much, it affects plant health, and algae moves in.

If you have undemanding plants, a stable ecosystem, standard intensity bulbs (not HO or overdriven), and plenty of light to start with, bulbs can last a very long time before any problems show up. I have some tanks with bulbs at least four years old, and no problems.

Otherwise, the useful life of a bulb can be shorter. Once algae shows up, it can be hard to get rid of. And you may not immediately suspect insufficient light to be the cause; standard advice for algae includes _reducing_ light, which in this case will only make it _worse_. So some people prefer to replace their bulbs on a fixed schedule, eliminating that potential problem altogether.


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## RukoTheWonderDog (Nov 11, 2011)

I used to have a very old 48" single T12 strip that I used on an unplanted african cichlid tank years ago. The bulb was possibly the original, and I think I used the same bulb for 2 years myself. 

I never replaced the bulb because it would not accept a T8 bulb (which I already owned). I used the light with a standard timer, and I never had a problem with algae until I left for vacation. During that time, my nitrate levels increased and I had an algae explosion. 

When I returned to normal feeding and water change routines, the algae decided to stay. I blacked out the tank which worked great for a few weeks. Even with huge and consistent water changes the algae always seemed to come back and hang in there. I pulled my hair out trying to figure out the issue. Then the bulb died and I was forced to replace it with another, new T12.

After that, the algae stopped growing. It didn't go away, but I did not see any new expansion. I did not have further issues with algae.

I never really questioned that the old bulb was the source of the algae. Not terribly scientific I know, but aside from the bulb, nothing else changed on that tank. 

If you want to read up on some interesting info about algae, check out guys that are into making algae turf scrubbers. They target algae growth using 2700k - 3000K bulbs; the lower kelvin rating is more conducive to algae growth. Fluorescent bulbs have a reduction in the intensity and kelvin rating as they age.


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## rballi (Mar 4, 2010)

I think it is more that there are certain spectrums that plants can't utilize and algae can, that is why old bulbs can cause problems?


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## Complexity (Jan 30, 2008)

This may explain a major algae problem I just recently experienced. My bulbs are very old (some as old as 7 years!), and I was just thinking of replacing them. I was thinking new ones would be better for plant growth and had never considered that they may be the cause of the algae I had, but this may explain things.

Over the last few years, my 75g tank went from a very heavily planted, high light, "high tech" tank with injected CO2 and all to one that was basically ignored. Of course, many plants died and I had to lower my lighting schedule. I added a number of crypts and let things go more low-tech.

However, after a year or so, I started getting spot algae on the glass. This is that really hard to remove small green dots or spots. I didn't worry too much about it at first since I was very busy at the time and wasn't working much on my tanks. I just cleaned it off every now and then and kept things like normal.

Over the next year, the spot algae got worse and worse and worse. It finally got to the point it completely took over the sides of the tank. I literally could not see inside the tank! The fish and plants inside were fine (I cleaned a hole on the side to see in), but the spot algae was so thick and so bad, it could only be removed with very strong scraping. Since I was already planning to tear that tank down and redo it, including bleaching everything, I chose to leave it as it was until I could clean it all up.

I could not explain why that particular tank got such bad algae, but perhaps the really old bulbs was partly to blame? I can't say for sure. I get some spot algae on all my tanks, and all my bulbs are at least 3 year old or older.

Looks like it's time to get new bulbs! I guess if the spot algae goes away with new bulbs, then I'll know for sure that it contributed to the cause.


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## crypto (Apr 12, 2012)

Hmm, maybe the old light bulb - algae connection is not a myth. It does seem strange that a reduction in light would cause algae, however.:icon_ques


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