How much does depth affect lighting level?? - The Planted Tank Forum
 
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post #1 of 15 (permalink) Old 10-19-2006, 03:10 PM Thread Starter
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How much does depth affect lighting level??

Hi all. I recently bought a 25g X-H (24" x 12" x 20") to take the place of my scratched up and aging 20H (24" x 12" x 16") - see signature. I figured the extra 4" of height would diminish some of the lighting, as the high light level has brought me endless algae problems. The light enclosure is also raised above the tank by about 3-4". My question is, will the depth affect the lighting level at all or does it not really play into it that much. Part of the reason I wanted to get another 24 x 12 tank, is so I can still use the stand and light enclosure from the 20H. I'm also planning on using aquasoil, instead of the fluorite currently in my 20H. I just can't seem to grow certain plants, and I'm hoping that's the answer since ferts are dosed on a regular basis along with weekly wc's (EI). I turned up the Co2 a couple days ago to the point where the plants were pretty much all pearling, but there's still the age-old problem of algae on some leaves, which I don't think will ever go away. Maybe AS and a taller tank will do the trick? I was also toying with the notion of getting the lights (55w x 2) on separate ballasts so I can run one of them for the full 12 hrs and just have the other come on for 5-6 hrs during the peak of the day. Ideas? I probably won't get this tank up and running for another few weeks, but I'm going to take my time with the planning and the hardscape. Hopefully pictures to come soon! Thanks.

-Ryan

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post #2 of 15 (permalink) Old 10-19-2006, 04:10 PM
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Height has a lot to do with lighting. The deeper the tank the harder it is to grow some forground plants. For me erios/HC. 55x2 is high light over a 20H but you should be able to controll the algae still. I have 96 watts of T5HO over my ADA 60cm (17 gallons) with no algae problems. I know someone who has 130 watts of powercompact over the same tank with no algae problems.


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post #3 of 15 (permalink) Old 10-19-2006, 05:24 PM Thread Starter
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I currently have elatine trianda that is doing pretty well and spreading, but I may also try HC when I get the 25 set up. As for the algae issues, increasing depth and tank size will reduce the wpg from 5.5 to a little over 4, which is the notion I was considering. I also know that people say to overdose Po4, but this has never worked for me. It actually makes it worse in some situations. Other than that, I'm not sure what else can be done other than perhaps switching to a mist Co2 diffuser, rather than the current PVC inline reactor.

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post #4 of 15 (permalink) Old 10-19-2006, 08:41 PM
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Quote:
Originally Posted by ringram View Post
I currently have elatine trianda that is doing pretty well and spreading, but I may also try HC when I get the 25 set up. As for the algae issues, increasing depth and tank size will reduce the wpg from 5.5 to a little over 4, which is the notion I was considering. I also know that people say to overdose Po4, but this has never worked for me. It actually makes it worse in some situations. Other than that, I'm not sure what else can be done other than perhaps switching to a mist Co2 diffuser, rather than the current PVC inline reactor.
One thing that is easy to do is to get a in-tank pH indicator and use it as a CO2 meter - see: DIY Drop Checker - Aquatic Plant Central- aquascaping...a living art
This will let you be sure that you are supplying an adequate amount of CO2 without guessing, trying to stop just short of harming the fish, etc.

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post #5 of 15 (permalink) Old 10-19-2006, 09:30 PM Thread Starter
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Very interesting Hoppy. Thanks for the info! It may be better to try that, since I'm a little lazy when it comes to testing. But then again, that's the whole point of EI!

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post #6 of 15 (permalink) Old 10-19-2006, 10:02 PM
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I did a bit of research on the question about light loss in water. If you have clean water, which you probably do with the filtration, you will lose about 1% of the visible light per cm of water. So, the extra 4 inches, or 10 cm causes a loss of about 10% more of the light. Then, there is the loss due to the light not being perfectly reflected down into the tank - some spills out the glass and is lost. That loss may be bigger, but it isn't proportional to the square of the depth. My guess is that is another 10-20% loss going the extra 4 inches. I don't consider these to be significant losses.

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post #7 of 15 (permalink) Old 10-19-2006, 10:59 PM
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It is a significant loss if you ever had a tall tank. Its more about intensity than anything else. Once a tank gets too tall its just hard for many plants to thrive until they get half way up the tank.


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post #8 of 15 (permalink) Old 10-19-2006, 11:24 PM Thread Starter
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Well, I know the light reflection is about as good as it can get. I have ah supply reflectors with 2 x 55w PCs. The reflectors may be a little dusty, but I'll clean them up good before setting up the tank. So, the *effective* light going into the tank will go from 110w --> 99w or so if its a 10% loss? That would still be around 4wpg for the 25gal, but its a easier-to-maintain range than 5.5 wpg. I'm hoping that I won't have any issues growing HC, glosso or whatever higher light foreground I decide to go with....something tells me that the light will still be plenty.

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post #9 of 15 (permalink) Old 10-19-2006, 11:37 PM
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to quote rex grigg:

"Ok, [rant mode on] I have seen a lot of people repeating the lie that deeper tanks need more light. That might be true if you are using crappy lighting systems or barely have enough light as it is. But if you use decent lighting systems with decent reflectors the depth of the tank doesn't mean squat. You might hear about spectral drop off or lighting decrease. Bull[censored][censored][censored][censored]! If your tank was 30 feet deep it would be one thing. But the difference between 18" and 30" is not enough to worry about as long as you have good reflectors. "


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post #10 of 15 (permalink) Old 10-20-2006, 03:44 AM
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At 20 inches, you probably will be fine with growing your plants. However, I did have some problems myself. I could not grow some plants in my 20" high tank with the same parameters as my tank that is 14"s high. With that being said though, in my new tank that is 18"s high I am not having a single problem. I still say there is a big difference in tanks with different heights, I don't agree with that quote on this point. (unless Rex considers my coralife lights to have crappy reflectors, I kind of do)


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post #11 of 15 (permalink) Old 10-20-2006, 04:09 AM
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If you have a lot of suspended solids in the water then all bets are off. But, then you should see cloudy water with the lights on. But, lacking suspended solids, the data show that in the visible spectrum, you only lose 1% or so of the light per centimeter. It would certainly appear that adding 4 more inches or 10 more cm to the depth of the water causes only an additional 10% loss of light. We don't worry about the fact that PC bulbs lose more than that just by being used several hours, so I just can't see how a 10% loss to absorption and scatter to the water can be significant. One vote here for Rex!

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post #12 of 15 (permalink) Old 10-20-2006, 05:50 PM
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Ian, I have a light meter, we can do a scale from the source at various distances,when you do a large water change, we can measure anywhere you want

110w on a 25 tall is about right.
That's what I used for several years.

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post #13 of 15 (permalink) Old 10-20-2006, 06:51 PM
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Ringram, FWIW - and I'm almost at a new tank level considering the amount of AS I added: 36 liters. I'm having more algae issues. The plants do like the soil, undoubtably. Some Downoi and Erios are growing well, but a hair/thread algae and some Diatom and Red algaes are flirting conspicuously with some of my upper reaching stems . I haven't been dosing much of anything. So even though I have a lot of mature stems, its almost like the tank is balancing out like a new tank would, to some degree.

I'm actually trying to shorten my light duration and upping the CO2 to see if that helps. Its a 216 watt Tek on a 24" tall 90 gallon.





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post #14 of 15 (permalink) Old 10-20-2006, 08:01 PM Thread Starter
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Well, I'm going to be switching the plants over from the 20H that is coming down. I'll use the existing filter, Co2 reactor(unless I go "mist") and UV, although it still may suffer the new tank syndrome with all the new substrate. I suppose I'll halt on dosing, or just dose 1/2 the normal amt for the first few days or week. I might even cut lighting down from 12 hrs to 9 or so, until the plants get going. I'm going to do a really good clean and polish of the ahsupply reflectors, just to make sure the light is reflecting as well as possible... Thanks for the help!
Oh yeah, and since my first post, I upped the Co2 (ottos are still a-ok), added a small powerhead and continued dosing daily. When I come home from work, all the plants are pearling! The e. trianda is spreading and bacopa monnieri is growing ~1" a day. Most of the others are doing well also. The myaca, which I haven't done well with in the past is pearling like crazy and sending off side-shoots. I'm still getting some algae on leaves of soem of the plants. Hopefully that will correct itself.

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post #15 of 15 (permalink) Old 10-20-2006, 08:59 PM
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I got a mini NH4 spike - so I had to add some Zeolite since I had the tank stocked with fish. I think most folks have had to go real easy on dosing at first, at least that is what I've heard from a few.





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