Old Bulbs = Algae

[MrGoodbytes]

Not sure what red is (0K?), but yellow is 5000K, ...

Not exaclty the answer to what the OP asked but I thought I would post this for curiosity's sake. The colour temperature (as some may know) corresponds to the peak wavelength of the radiation of a blackbody at that temperature. To find this wavelength (should you be so inclined), you can use Wien's Displacement Law:

wavelength (meters) = 0.002898 / temperature (Kelvin)

So a peak of 700 nm (very red) corresponds to about 4,140 K.

[chris88]

To make it really simple. Algae need a few things to survive and thrive.
-They need light to photosynthesize (especially red light or low kelvin color light like 6,500k or lower)
-They need nitrates, fish crap and decomposing waste, some water sources can have high nitrates to begin with
-They need phosphates, most flake and frozen food, sometimes from tap water or a bad ro membrane.
- And sometimes certain algae use silica to their advantage (mostly diatoms)

If you are getting an algae bloom and your bulbs are old it will not necessarily fix the problem. It might help if you get new higher Kelvin bulbs like 14,000k or 20,000k but they real key to eliminating algae is to lower your nutrients. Try reading about carbon dosing, increase your water changes, feed less, get a bigger skimmer, etc.

[Myka]

Originally Posted by MrGoodbytes

Not exaclty the answer to what the OP asked but I thought I would post this for curiosity's sake.

So a peak of 700 nm (very red) corresponds to about 4,140 K.

Thank you for posting this, but it doesn't make sense...? I have some household bulbs that say 3500K on them and they are not red. Am I missing something?

----------------------------

Chris, the OP didn't ask "why do I have algae?". The OP may not have any algae at all. The OP asked "I've heard that old MH bulbs can be a contributing factor to unwanted algae growth. Could someone explain the theory behind algae growth?" There are nuisance algae threads all over the place (my signature for example lol).

[Bloodasp]

Doesn't make sense either. Graphs I've looked at show red being at 1000-2000k

[chris88]

You can't really compare Nm to kelvin. Red is from 650-700nm but that doesn’t correlate to a Kelvin tempter. A lower Kelvin light will have more red in its spectrum but that doesn't mean the bulb is going to look red. Just like a 10,000k bulb has a lot of green light, it doesn’t mean the bulb looks green. A 2,700k bulb will have a warm oranage-ish yellow hue almost like a candle light, while a 20,000k barely has any red spectrum in it and is predominantly blue. Most mid range bulbs have spikes in different spectrums which makes the color look white because of the way they blend. (6,500k – 14,000k)

[Myka]

Graeme, it is still interesting information that's kinda on-topic. the bulbs we use are usually "rated" at a certain color temperature, but if you use a CT meter it will say the color is much different. I don't fully understand why we see it as a different CT than the meter does? Must have something to do with the spikes in the spectrum over-powering our eyes maybe...?

Originally Posted by chris88

Just like a 10,000k bulb has a lot of green light, it doesn’t mean the bulb looks green. A 2,700k bulb will have a warm oranage-ish yellow hue almost like a candle light, while a 20,000k barely has any red spectrum in it and is predominantly blue. Most mid range bulbs have spikes in different spectrums...

That's why they are called "full spectrum". Some are "fuller" than others though. I think most people know that all the colors in the rainbow are in "white" light.

[RuGlu6]

My T5 bulbs are 3+ years old. Replaced only when burnt out.
Have 6xTek T5.
My tank has almost non existent algae.
My SPS have VERY nice color and growth I have Pink, bright green, blue tip Dual Color SPS and green tip as well.
So go figure.

Low bio load (only 3 fish in 65 gal tank ), high ORP (with high air flow) air driven skimmer it is constant just over 450. Second skimmer is Deltek 600 HOB.

[MrGoodbytes]

Hmm interesting. I looked into it further with respect to fluorescent lamps in particular and it turns out to be quite a bit more complicated to determine actual correlated colour temperature (CCT). They use CCT to distinguish between actual CT since our lamps aren't actually radiating at that temperature.

You can use Wien's Law to find the peak of the blackbody spectrum which that of the lamp resembles but the lamp's spectral distribution (intensity per unit wavelength) will be different, due to the phosphors. Nevertheless, it still produces light that looks similar to our eyes, which "add" colours. That's why a low CCT lamp may appear white-"ish" but have a peak in the red - the other colours are playing a part when we observe them altogether.

Bah, sorry if this is way off topic or anything. Hope this clears things up somewhat.

Graeme

[mark]

Is it shift in temperature, 14K to 10K, don't see a problem as lots start with 10K bulbs, or they basically stay at 14K but with just a increased narrow spike at a lower wavelength.

(or just a conspiracy by the manufactures and supplier to replace our bulbs)