Is Ultra-Actinic light beneficial for freshwater plants?

[Mitsy]

I came across a good deal on a PowerCompact hood that fits my 29 gallon (110 liters) tall (71 centimeters deep) aquarium. Since I am trying to grow lots of plants it seemed like a good way to provide a better souce of light than the two 18 watt regular fluorescent tubes I was using. The hood came with a 32 watt 10,000K Daylight and a 32 watt Ultra-Actinic, which I understand to be mainly for the health of reef organisms. Will it be useful to use it (it makes the tank look odd) or should I be looking for another tube to replace it?

[Ira]

I think it'll be an improvement over the 18 watt just because it's twice as much light, but it won't be ideal. I think the ideal color temperature is 5000k? Definitely sounds like the setup for a small reef tank, but wouldn't be bright enough for that. Anyway, should at least be an improvement.

[kluyu]

I agree with Ira that it would be an improvement over the older setup. The actinic lights usually have a large spike in the blue end of the spectrum, which is what many marine algaes and corals like/need to grow.

Freshwater plants also like some light in the blue spectrum, but generally prefer larger spikes in the red/orange end of the spectrum. There is some evidence that they also like a bit of a spike in the green areas, but this is mostly still in the "hypothesis" area.

So, you have upped the correct intensity of light with the 32 watts. Since you have a tall tank (I have one & it gives me problems) the amount of that light that is actually hitting your substrate is reduced.

(BTW, if you would like to read a discussion of whether or not light is diminished by depth of tank, I refer you to this link. The conclusions some of the contributors reached do not match my "hands on" experience with tall tanks, but it is a good discussion, nevertheless.)

http://www.thekrib.com/Lights/depth.html

There is some data that indicate that algae prefer the blue end of the spectrum. (this is just something I picked up in general reading & haven't tried to verify).

The K number is not, in my experience, very important in plant growth. The correct spectral output and the correct intensity is. You usually see K numbers from 5000 to 6500 recommended. These K numbers just represent what color noon-time sun is in the temperate zones to the tropical zones. There are many combinations of spectral spikes that will give you the same K number, but have different effects on your plants.

[Warren]

Watch out for too much blue light - UV. It may cause excess green algae in a freshwater tank.

[john1]

Hi Mitsi

Can you be more specific reg the measurment about your tank?

I've got a 3' tank, which is 40cm tall. And it holds 125l. According to your tank's height of 71cm, it must be a very narrow one. According to your height you probably need much more wattage to reach the bottom.

John

[Mitsy]

I have traded the ultra-actinic for another 10,000 K tube, it was the only type the local FS had, and I didn't want to spend another $15-$20 to order a tube.

So, now I have 64 watts total, a much more appealing appearance, still having some algae problems, but it is gradually diminishing (the soft brownish kind).

I am running one tube about 11 hours a day and the other about 7 hours because it is on the circuit with the fan which is VERY annoying, and I keep it on only when no-one is home during the midday.

I have mostly easy to grow plants and easy to keep fish, and they seem to be doing fine.