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Old 10-21-2011, 06:41 AM   #15 (permalink)
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Default Re: PAR data collection

So an outdoor pond's PAR value is 800 at the substrate (at 2' water depth). How can I have a tank that is so brightly lit at the substrate? How much light do I need? Can I keep it clean and algae-free?

Let's look at Michael's 40 gallon tank (36" x 15" x 16" tall). It's not 2' tall but it is about 3/4 of that. So I will need a PAR reading of 600 to simulate an outdoor pond's 800 PAR hitting the bottom.

And here are the (amusing) numbers:

Michael's tank with 2 light fixtures on top (70 watts of light) receives 97 PAR:
"@ substrate: Measurements with both fixtures: w/ glass 83, w/o glass 97"

So 70 watts = 97 PAR at the substrate.
=> To get 600 PAR to the substrate we will need 6.2 times the light he has now.
6.2 x 70 watts = 433 watts!

No fluoresent bulbs can be crammed on top of a 40 gallon tank to add up 433 watts of light. There isn't enough room. You will need a 400 watt Metal Halide. Now imagine - a 16" tall tank with a huge, hot, 400 watt Metal Halide on top. Right... You are better off just placing the tank outside, under the open sun.

And here's my usual attack at popular half-baked approaches; I want to see a 40 galon tank with 433 watts of light use EI or PPS. In other words - "How do EI and PPS relate to Nature?". Since they are such great and so popular approaches they should let you take care of such a Natural tank, right? Of course not. Needless to say there will be ultra-fast plant growth (4" a day not uncommon with stems), deficiencies developing overnight, and insane work to keep up with this speed demon of a tank in some resemblance of a balance.

Or... You can emulate the outdoor pond:
1. Rich substrate
2. Good flow
3. Water void of nutrients

Game over. If you care to think, that is.

Funny thing, if you go on one of Australian planted tank forums and look for the pictures of the guy that has an outdoor aquarium plant growing facility you will see exactly that: Sun blasting the super clear water, good flow, and tons of super healthy plants... Ah yes, almost forgot - and MUD on the bottom. That's it. How novel.


Last edited by niko; 10-21-2011 at 06:54 AM..
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