# Converting open air PAR to water



## GadgetGirl (Sep 25, 2013)

I just purchased the 36" Finnex Planted Plus 24/7 CRV series which is being delivered tomorrow. The website states it's fully customizable (color and intensity) at all time changes. They give a nice PAR table (see pic)for the different size lights and depths but it's in open air values! Is there a reasonable way of estimating the actual PAR in water? I'm clueless as to how much to dim it. Tank is 13.5 in from top to substrate level and is *heavily* planted. No CO2 of course. Thanks for any advise!

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## GadgetGirl (Sep 25, 2013)

For 13.5 in, would a 50% decrease in the intensity work? It states approx 70ish open air PAR at that depth. I figure up to 30 for low tech. 

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## mistergreen (Mar 3, 2007)

Hoppy knows the answer specifically. 
From what I can remember, water in our aquariums, a few feet don't diminish PAR much. The walls of the aquarium reflects the light back into the tank so increases PAR a little.


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## GadgetGirl (Sep 25, 2013)

mistergreen said:


> Hoppy knows the answer specifically.
> From what I can remember, water in our aquariums, a few feet don't diminish PAR much. The walls of the aquarium reflects the light back into the tank so increases PAR a little.


I didn't know that! I just assumed water would decrease it. But maybe that's at great depths like lakes and rivers.

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## mistergreen (Mar 3, 2007)

Lots of particulates in rivers too so that'll block out light.


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## GadgetGirl (Sep 25, 2013)

mistergreen said:


> Lots of particulates in rivers too so that'll block out light.


True!

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## GadgetGirl (Sep 25, 2013)

Summoning @hoppycalif


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## hoppycalif (Apr 7, 2005)

I just saw my BatMan light flashing in the sky!!

Clear water doesn't significantly reduce light intensity for distances up to at least 30 inches. But, if you keep the glass walls of your aquarium clean on the inside, and clean and not painted on the outside, you can get a big boost in intensity from light reflected off the glass to air interface. My LED light gives about a 50% increase at the substrate! Lights with reflectors will give a much smaller increase. Also, when a strip light is over the center of the tank, the refraction of the light as it goes from the air to the water also increases the intensity by a small amount.

I suspect most of us do not wipe the inside of our glass walls every day, so it is probably the best idea to just assume that the PAR in air is the same as the PAR in water. It is also much easier to measure PAR in the air than in our aquarium filled with water, let alone in a fully planted aquarium. To further complicate this, Apogee went for years insisting that their PAR meters read the same in air and water. A few years ago, when they improved their PAR sensor, they found that there is a big correction that needs to be applied when using their meters in water - about a 15% correction, making their PAR readings 15% too low when used in water. This correction is a function of the refraction as the light goes through the water to diffuser interface, and that is also a function of the curvature of the diffuser. When I was making PAR meters, I ran into this and ended up by giving up on making them, because I couldn't meet Apogee's "same reading in air and water" standard. (I also got too much arthritis in my hands to continue.)


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## GadgetGirl (Sep 25, 2013)

Thanks Hoppy! Interesting! That must be what I recall, that it is a limitation of the meter itself not that the actual PAR value was different. I try to keep the interior clean but I do have a bit of green dust algae. And I have light colored play sand cap.
Right now I have the original version Planted Plus 24/7 on 4 in risers. So, do you think decreasing intensity by 50% would do it? I love that this newer version is so customizable! Their chart shows about 70ish PAR at approx 13 in. I'm assuming that's at the full intensity.

Edit for typos.


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## hoppycalif (Apr 7, 2005)

I found that a low light, non-CO2 tank, using Excel for carbon, will do pretty well at 35-40 PAR at the substrate. That table of intensity for each length of light fixture, and at various distances suggests that you will get about 60 PAR at about 13.5 inches. And, you would get about 35-40 PAR at about 22 inches from the 36 inch long light. All of those PAR numbers could easily be off by +/-5 PAR.


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## GadgetGirl (Sep 25, 2013)

I've actually started using Excel with this tank. Never used it before and thought I'd try it. 
I'm going to aim for about a 50% reduction with this light and tank combo. I'm looking forward to getting this light and tweaking it. A lot of people don't like it cause they can't figure it out but I shouldn't have too much trouble. I do home automation and I understand lights ramping up and down! In fact, I loosely match my Hue lights to the aquarium's 24/7 schedule. Lol


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## hoppycalif (Apr 7, 2005)

I suggest that you ignore the Excel dosing schedule on the bottle. Instead, just dose 2 ml per 10 gallons of water every day. *Do not dose 5 ml per 10 gallons at any time.* If you have any of the plants that are sensitive to Excel, the 5 ml dosing will harm them considerably - Vals, for example. And, 1 ml per 10 gallons isn't enough to provide the needed carbon.


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## GadgetGirl (Sep 25, 2013)

That's exactly what I've been doing! I have a 40g tank. I figure with soil and sand displacement I have about 31 g of water. So I've been dosing just a tad over 6 ml in the mornings.


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## hoppycalif (Apr 7, 2005)

GadgetGirl said:


> That's exactly what I've been doing! I have a 40g tank. I figure with soil and sand displacement I have about 31 g of water. So I've been dosing just a tad over 6 ml in the mornings.


Very good! That worked well for me.


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## GadgetGirl (Sep 25, 2013)

Well I got the light yesterday and set it up this morning. I am very excited about this light! I set the noon to 3pm intensity of white & RGB to 50%. That should give me about 30ish PAR for my 13.5in depth. I decreased the intensity a bit for 9pm and set total darkness between midnight and 6am. Then at 6am it will ramp up to the 9am setting which I didn't tweak. So far, I highly recommend!
Edit: I feel like Finnex addressed all of the shortcomings of the 1st 24/7.


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