I'm confused - WPG vs. k rating...

rainbowcharmer

rainbowcharmer

AC Members
Jul 30, 2007
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So in my 75 gal tank, I want a low-light planted look. The bulb that came with the tank was I believe 40 watts, and it looked horrible. The plants I put in were dying, and I know that the WPG was definitely not enough.

Problem is, I cannot figure out how to get over 1 wpg in this tank.

I bought a 4 foot shop light that holds 2 T5 bulbs (32 watt each, daylight 6700k). The reflectors inside the shop light seem great - and the tank is super bright now (at least compared to what it was before). But at 32 watts each, I'm still less than 1 wpg, and I have zero room left over my tank to put more lighting. I was going to line up the individual strip light that came with the tank to add another 40 watts, but there is just not enough room to do that and still be able to actually access the tank at all. Is lower wattage but using the ideal bulbs that are 6700K ok? Is WPG more important or is having the daylight bulbs more important?

I guess basically, is the fixture I bought going to be sufficient? If not, how do I add more wattage and still have access to the tank? The plants are growing back, and it looks really nice, but I'm just worried that it may not be enough.

This is strictly a low-light tank - no CO2 or anything fancy. I've got crypts, some dwarf sag, hornwort, etc. Nothing real fancy, but obviously I want it all to survive.

Please advise??
 
i would return everything, get your original strip light that came with the tank, rip out the insides, replace everything (including wiring and maybe even add a fan) with 90 watts of 6700K CFL. Search the DIY section on the forum for a more detailed 'how to'

Also WPG v K....it is like comparing apples to oranges.
K: to only touch on the basics of basics: refers to the spectrum (kelvin, temperature) of the bulb. which needs to match what you havein your tank (e.g., actinic lights, 12,000k, or 2400k lights will all be relatively useless in a planted tank). Plants like ~6700k so that is basically what you need to provide them.

WPG: is a relatively accurate inaccurate rule of thumb in gauging how much light is on top of your tank, it also is relatively accurately innacurate in describing the light needs of certain plants. WPG gets thrown completely out the window when you have very small and very large tanks. To grow certain plants you need about 1WPG at minimum and 4WPG at maximum. so yea. between 1-2 is good.

Summary: 30WPG of actinic lights over a tank will be useless because it is the wrong spectrum. 0.2 WPG of 6700K light is useless because you dont really have enough light over the tank even though it is the right spectrum. 4 WPG of 10,000K light will give you really good growth although soem of the specturm is out of range (debatable) and you might be able to consider it 3WPG. at this alter point you NEED co2. co2 is a whole different can o' worms. 1.5-2WPG of 6500K light is ideal IMHO.

(note: this is my theory, many peoples theory differs)
 
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the shop lights are normal output. The same bulb in a High Output (T5HO) fixture gives you the 55 watts.
 
Msj - where did you find your fixture at? At Lowes, where I got mine, this was the highest wattage in a 4' fixture that I could find.

As for retro-fitting... I'm not so much on the handy man type stuff... And I don't know anyone locally who is. My dad could do it, but he's an 11 hour drive away... Whatever I do has to be pretty plug and play for me to be able to handle it... That stuff at ahsupply looks a little scary??

Help!
 
You should be able to find something that you can mail order online. There are many many knock-off type T5HO units available for very little money. And pretty good units for what they cost, too. I have a 3ft 2x39w T5HO 10,000K, made in China or someplace, that cost me $105. And that's Australian dollars, btw. Cheap as and does the job perfectly.

I am having trouble picturing how big your current light fixture must be that you can't add any more lights above a 75...???

As to WPG vs K goes, coach got it pretty well right. However, anything between 6,500K and 10,000K will be fine... Have a look at this article by Rex Grigg. Should give you a better idea of how lights (and the whole wpg rule) really work...
 
rainbowcharmer said:
Msj - where did you find your fixture at? At Lowes, where I got mine, this was the highest wattage in a 4' fixture that I could find.

As for retro-fitting... I'm not so much on the handy man type stuff... And I don't know anyone locally who is. My dad could do it, but he's an 11 hour drive away... Whatever I do has to be pretty plug and play for me to be able to handle it... That stuff at ahsupply looks a little scary??

Help!
Click to expand...


I got mine at www.thatfishplace.com. I think its made by AGA.
 
Think of K rating as a number that means absolutely nothing. Now take WPG... that's a number that means almost as little as K value...

K is a term that describes the color of a light if that light were a star burning at that temperature. It has been perverted and distorted to make a oink bulb burn in the 9000K range, and a blue light burns at 6500K. It really means nothing. Get a bulb that makes your tank look good and you have the right bulb.

Now as for watts per gallon. You should, theoretically run around 5 watts per gallon of standard t8 fluorescent with pressurized CO2 to get optimum performance. The problem is, who runs t8s these days (besides me, but I overdrive mine). The cheapest best lights are overdriven t8s, here is the howto:
http://www.gwapa.org/articles/ODNO/

The problem with getting into overdriven t8s, is that you can no longer use terms like "wpg" because I dont exactly know how much wattage is being pumped, and how much additional light is actually being generated. All I know is that four overdriven bulbs with pressurized CO2 makes my tank look like club soda with all the pearling.
 
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