lighting requirement for 90g tall

[teamgs]

Greetings,
I had my 96W dual daylight CF give out and am looking at what to replace it with. I am only growing low light plants, and no CO2, and have been running 1 - 96W dual daylight CF and 1 - 50/50 actinic/daylight. The 90G "tall style" tank depth is 30" to the gravel from the light.

I have had issues with algae, and have been thinking about lowering the lighting some. I calculate that I have 144W, and thought this was fine, but now I read that CF's should be calculated at more like 175% towards the WPG rule. Top this off with the posts that state that 50% of light is lost at around 24" depths, and I am getting confused.

Let's say that I replace my dual daylight with a 96W 50/50 daylight/actinic. This would put me at 96W. 96 * 1.75 = 168W. 168 /2 = 84W at the gravel. Does this sound decent for a standard low light tank? Or should I stay with the dual daylight 96W which would give me 144W. 144 * 1.75 = 252 . 252 / 2 = 126W at the gravel?

Hope this makes sense, and you can give me some advice.

Regards,

Gary

[Purrbox]

Here's a link that I think might be helpful to you. There's a calculator about halfway down the page. Once you enter the measurements from your aquarium it will give you an estimate of how much light you would need of certain types to hit various target light levels.

[teamgs]

Thanks for that link!

It doesn't take into account depth, however. Don't you think this has an effect, since my tank depth is 30"?

The link said that my tank was right at very high lighting.
Regards,

Gary

[Purrbox]

What are the length and width of your aquarium? Those results don't sound right.

[teamgs]

My tank is 35" x 17" x 31" tall .

Actually, I misread the results. At 144W I am right in the middle of high and very high.

regards,

Gary

[Purrbox]

Okay the raw results for your aquarium are:
Compact Fluorescent
168W - VeryHigh
127W - High
84W - Moderate
42W - Low

The note at the bottom says to add 25% for every 4" above 24" in height. You aquarium is 6" above 24", so that would be 37.5% resulting in:

Compact Fluorescent
231W - VeryHigh
175W - High
116W - Moderate
58W - Low

Since Actinic usually isn't included in the amount of usable light your levels would be:
100% Daylight (192W) - High to Very High
75% Daylight (144W) - Moderate to High
50% Daylight (96W) - Low to Moderate

Based on these estimates, I'd say that cutting back on your light as you've suggested may help with your algae issues.

It could be that something else is causing the issues though, so I wouldn't automatically assume that the amount of light you're running without CO2 is definately the cause.

[teamgs]

Thanks for the assistance! I missed the part regarding the 25% per 4" above 24". Must have been reading too fast.

I think I will get another 50/50, giving me 96 Watts. The only downside is that the current USA Sunpaq 50/50 have only 10000K white light, where the dual daylight (no actinic) have both 6700 and 10000K light.

I guess I can always look for another brand.

Thanks Again!

Gary

[Purrbox]

If the bulbs extend the entire length of the aquarium you could either just remove on of the bulbs (if your fixture can run this way) and run a single Dual Daylight, or run a Dual Daylight and an Actinic.

[teamgs]

My bulbs do indeed run the length of the aquarium, however there are only two light sockets. The fixture is set up for two dual light bulbs. I can go with a lower wattage bulb, but they are shorter and would only cover about 2/3 of the tank length.

Assuming that there isn't much of an issue with using a single wavelength bulb over a dual wavelength one, I will probably just get a second 96W 50/50 actinic, which will give me 96W total of light.

Thanks again, I really appreciate your help.

Regards,

Gary