Looking for comments on my light level

[Oreo]

I have a 110gal extra tall tank. It's dimensions are 48" wide by 30" high by 18" front to back.

I've got a light fixture with four 48" T5HO. The bulbs can be turned on / off in pairs. I've been running a 10hr photo-period.

So if my math is correct, with one pair of bulbs on I've got 108w which is 1wpg for a "low" light level. But before CO2 every plant in the tank was covered with black algae. Now I add CO2 and the algae seems to be kept at bay. Plants aren't growing gang-busters but they do grow. Now, if I turn on the second pair of bulbs for 216w, for 2wpg (should be medium light, right?) I seem to notice the black slime algae growing on the leaves & rocks again.

My ferts are perfect- I've got access to lab grade testing equipment. I've got the CO2 cranked up to just a little less then fish gasping at the surface and I'm adding twice the recommended dose of Florin Axis (liquid carbon supplement, not the same as excel.) My pump turns the tank volume over about 7 times an hour.

The only thing I can think to question is that there's something with these T5HO bulbs that put out so much light that the wpg guide doesn't hold up.

Thoughts?

 

[dutchy]

The WPG guide never holds up. I think it's one of the most misunderstood aspects in this hobby. The only way to measure the right amount of light is with a PAR meter.
I measure light with a PAR meter and found out that T5's are pretty intense lights that give more output than most people think. With 4 tubes on an 18" deep tank I really think you have enough light, even when it's 30 inch high, but only if you use good reflectors. But I don't think just 2 tubes would be enough.
But that's just because it's 30 inch high.

regards,
dutchy

 

[Oreo]

Well, to be honest, the reflector is pretty crappy. Just a single piece of mirrored film behind the bulbs. Nothing parabolic. But when you say "enough"... enough for what? IIRC, Tom Barr advocates that any light level is appropriate- up to a point, as long as the nutrient & CO2 levels are good & in balance. The nutrient levels I have 100% confidence in. CO2 is as much as my fish can tolerate, but I don't yet have a drop checker.

 

[aquabillpers]

The original "two watts per gallon" rule was based on T12's. Newer bulbs put out more light energy per watt. I believe that T5's produce about 1.5 times the energy as do T12's of the same wattage, so 2 WPG of T5 light is the equivalent of 3 WPG under the old guidlines. I don't know how much more, if any, the "HO" adds.

I agree that measuring with a par meter is preferable to the WPG rule. I'd think that by now someone would have published a comparison of the PAR (or lux) readings of various bulbs at various depths.

Bill

 

[csmith]

I had the same problem, Oreo. Watts per gallon really messed me up for a while. VaughnH/Hoppy (same person, different forums) has some really user friendly explanations. Mixing watt per gallon and T5HO is probably the biggest mistake I've made thus far.

http://www.plantedtank.net/forums/lighting/105774-par-vs-distance-t5-t12-pc.html
http://www.barrreport.com/showthread.php/6036-Massaged-PAR-Data-for-T5HO-lights

Everytime I see your name on a thread I get hungry. Weird.. Anywho, Gerryd's post at the end of this thread really drove it home for me.

 

[Tom Barr]

I have a 120 Gal tank, close to the same volume, dimensions etc.
I use 4x 54W giesemann/Tek at about 10" above the tank which is 24" Tall , 24" Tall, 48" long.

It eats more CO2 than the other tanks which have even high lights, about 14" and PC lights.
PAR is about 20micromols higher.
The same shop light T12's = 3x the wattage to get the same PAR at the bottom of this tank.

So I'd need 600W or more of T12's to the 216w I have.
Only by testing over distance and looking at spread using a light meter with a comparable unit, can we compare tanks and lights in real planted aquariums.
Can you guess and estimate some? Sure.
But this guessing and estimation shoukld be backed up with extensive testing and experience.

I did this for EI before I gave advice.
Same for lighting.
And the same is also true for current/CO2.

Regards,
Tom Barr

 

[dutchy]

But when you say "enough"... enough for what?

Sorry that I didn't specify. Enough means more than the level at which plants still grow, on my PAR meter around 40 micromol. Just 2 tubes without reflectors give me 35 micromol at 22 inch of height. Since your height could be something like 26 inch, the value could get under 30 micromol, which could mean your plants are at or reach their LCP point.

regards,
dutchy

 

[I Love Aqautic Weeds!]

Would anyone hazard to guess what PAR "range" I might be in with the 4 T5 Normal Output lights I run on my 46 bowfront. There are 4 T-5 bulbs 21 watts each, totaling 84 watts putting the tank at 1.8 T-5 watts per gallon.

Thanks,

Shawn

 

[dutchy]

Sorry I thought I could help you but I have no readings for T5NO lights.

regards.
dutchy

 

[Oreo]

I appreciate the replies. Turns out I must have forgotten just how powerful these T5HOs are. I know when I bought my light fixture I was planning for high-light capability in preparation for the day I started adding CO2. I must have forgotten the original lux calculations I did. A little googling last night helped me remember just how much light I have.

What's the dimensions of your 46 bow-front there Weeds? There's a formula for a rough estimation of lux based on hight of a bulb and the area it's gotta cover.