Old Bulbs = Algae

[wickedfrags]

No significant correlation between bulb age (or spectrum) and algae growth in my experience. Water quality (nutrient levels) dictates algae growth, not quantity or spectrum of light.

Originally Posted by Tyler Werbowski

I understand that older bulb lose intensity and there's a slight spectrum change. I've heard that old MH bulbs can be a contributing factor to unwanted algae growth. Could someone explain the theory behind algae growth?

[Myka]

If everything else is in order, the bulb age and spectrum will have no effect on algae. On a tank that already has an algae issue a change in bulbs and/or spectrum can really help. On a tank on the brink of an algae bloom aging bulbs can be the straw that broke the camel's back.

My tank is a very good example right now. One of my 20K halides burned out. I only have 10K as spares. So my reef has a 10K on the left side (with 6 months use on it) and a 20K on the right side (with 14 months use on it). On the left side a minor dusting of diatoms shows up in late afternoon under the 10K bulb, but not on the right under the 20K bulb. Also, you can see a difference that there is more to scrape off the front glass on the left than the right.

[chris88]

The shift in spectrum isn't the issue with old bulbs, it's the major drop in par. Its on average about a 30% drop in par after 6 months and sometimes a 50% drop after a year. This happens with t5's or halides. This isn't a debatable issue. There is a lot of data on the decrease in par so its a fact and not a conspiracy. I would not suggest running any type of bulb for longer then a year unless you are doing a fowlr tank. I change my t5's at about 9-10 months.

[Myka]

Originally Posted by chris88

The shift in spectrum isn't the issue with old bulbs, it's the major drop in par. Its on average about a 30% drop in par after 6 months and sometimes a 50% drop after a year. This happens with t5's or halides. This isn't a debatable issue. There is a lot of data on the decrease in par so its a fact and not a conspiracy. I would not suggest running any type of bulb for longer then a year unless you are doing a fowlr tank. I change my t5's at about 9-10 months.

It is a debatable issue because your numbers aren't right, but that's a different topic. Please explain how lower PAR affects algae growth...?

[chris88]

My numbers are close to right on, but it does change depending on the type of bulb and cooling of the bulbs. Just check reef central there are numerous threads on par decrease over time. I guarantee you my numbers are on par with what everyone has been testing and coming up with.

I didn’t make any mention of how par effects algae growth. My comment was directed to the people who said there was no need to change their bulbs unless they burn out. I already address effects color spectrum has on algae growth in my previous posts.