T5 question

okay, i have a 20 gallon long so my depth is fairly shallow. I have two coralife t5's over the tank. Theyre rated at 18watts per, one actinic one 10k.. my question is, i see so many people talking about 150 watt this 75 watt that. How can my tank be surviving off of only two 18 watt bulbs? ive also seen mention of t5 HO lights, are there two seperate kinds of t5 bulbs? I asked the LFS where i bought the bulbs if i needed stronger lighting for my corals and he said anymore than that would be overkill. He said T5's cant be rated on their wattage cuz theyre a different type of light, so im confused. But i cant see hanging a 150w MH over my tank, it seems like it would fry everything!! anyhelp would be appreciated..

 

There is a difference between regular T-5's and HO T-5's. For corals you will want the HO T-5's. You can probably keep some low light softies with your current lighting but I dont think any hard corals will survive IMHO. You can definitely do a MH light on your 20g tank. You can do a hanging fixture.

 

From what I've read it seems that the light a t5 bulb produces is efficient. The amount of lumens is high for the wattage. I don't really know the technical side of it very well though.
I have 4 24" t5ho (96w) above my 54g tank and it does well. I don't keep any sps in my tank though. I recently bought 4 new bulbs t5vho at 40w per bulb (160w). I'm going to see if my fixture can push the extra wattage.

 

Let me try to put it in perspective for you!!!! Your tank and its inhabitants can survive for extended periods of time because light IS NOT the ONLY essential ingredient to a successful and healthy tank! Other variables such as water quality and filtration represent other aspects that MUST be looked at and addressed in order for you to have continued success with your tank.
When you look at light, you have to decide on the types of coral you plan on keeping first of all,as corals require different lighting schemes, especially same species, because they can be found at varying depths in the reefs of the world. Unfortunately this is hard to determine, as many times we really don't know, where our coral is from, not to mention the depth the coral was collected from. This can pose a problem which is another reason why acclimation is so important! We can mold many corals to grow in light conditions that are usually not associated with that particular coral!
Now, having said this, in terms of the light intensity and overkill. Think of the irradiance of our reefs under the intensity of the sun on a cloudless sky. The lux of the sun is roughly 120,000 lux at the water's surface(lux is the measurement of the lumen...light energy shining at a given area over a period of time). Even at 15 feet in depth, the lux is around 20,000 lux. Obviously, our lights are not that bright and intense. What I am trying to get at that most of our corals can handle intense light, more so than our lighting schemes replicate.
The nice thing also is we have ways of placing corals either higher or lower in our tanks to support the health of our coral in terms of lighting irradiance. We also can raise and lower our lights many times above our waters surface to achieve the best lighting arrangement.
The reduction of excess nutrients, DOM, salt creep on our covers or lighting protective glass, suspended particles and Glebstoff(yellowing tinge to your water) among other variables will go along way in focusing the most PSR(photosynthetically stored radiation) amount of light actually harvested and converted to energy by our corals through photosynthesis. I know that some of our corals and other animals are not photosynthetic(contain zooxanthellae), but they will also survive various lighting schemes.
Hope this helps without getting to indepth!

 

Part2:
Many kinds of coral will adapt or should I say their zooxanthellae will adapt by the corals either changing to a different strain or zooxanthellae or zooxanthellae becomming more populated. At any rate many of them will acclimate fine, while others will bleach and waste away. Corals will in essence just take on a more subdued and faded color in their polyps as a result of limited light.
Example, I have green montipora digitata. I use to have power compact lighting, the color of the polyps were a brown with a hint of green! Since swithcing over to halides the color of the six different colored digitata and other Montiporas has become very vibrant and beautiful....

 

Let us know what you decide to go with in terms of lighting!