Increase lighting vs lower co2 - The Planted Tank Forum
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post #1 of 6 (permalink) Old 01-21-2013, 07:21 PM Thread Starter
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Increase lighting vs lower co2

I recently added DIY co2 to my 20gallon high. I had been planning on upgrading lighting to something like finnex ray 2 from my current 4 t5no. I didn't do the lights because of concern about not providing enough co2. Turns out my co2 levels are at about ~45ppm consistently. I could fiddle with my recipe and bring that back a bit, question is, can I instead upgrade my lights which would allow the plants to utilize the higher levels of co2? Would that in fact lead to lower co2? Not sure it works that way.
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post #2 of 6 (permalink) Old 01-21-2013, 07:44 PM
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Almost all of the CO2 we inject into our tanks just escapes from the water surface. Only a small part is used by the plants. That means, adding more light, so the plants can grow faster, doesn't cause the CO2 level to drop significantly. Why do you think you have 45 ppm of CO2? That is unusually high for DIY CO2.

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post #3 of 6 (permalink) Old 01-21-2013, 08:35 PM
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I agree with hoppy. Plus 4 t5 no on a 20 g? What is the wattage? I would think that is more than enough light
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post #4 of 6 (permalink) Old 01-21-2013, 10:02 PM Thread Starter
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I got the co2 est from measuring ph (which looks to be about 6.4/6.5) and kh (4). Looks like that puts me somewhere between 37 & 47ppm co2. The lights are 4 t5NO 14w 6700k. I figure that puts me in the medium light level. On a 20g high, from research I've done/lights I've got, I'm looking at about 35 par at the substrate level. My goal has been to transition to high light. If I can pare back the co2 to about 25ppm on a consistent basis, I should be able to go high light right?

(Btw, I know I don't NEED to go high light, but I'm just in that phase of tinkering, experiencing different setups)
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post #5 of 6 (permalink) Old 01-21-2013, 11:28 PM
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You can't tell how much CO2 you have by measuring the pH and KH of the tank water. You can use a drop checker, with 4 dKH water, made from distilled water with nothing but baking soda in it to reise the KH to 4 dKH. Even that will only let you estimate the ppm of CO2 to be within the range of about 15 to about 45 ppm. Accurately measuring ppm of CO2 is very hard to do without spending a lot of money for professional equipment.

If your fish are not gasping for air at the water surface you probably have less than 40 ppm of CO2, but that could be 10 ppm on up. If you want to go higher in CO2 you need to be sure you have good oxygenation of the water, by having the whole water surface well rippled, as a start, and you need very good water circulation in the tank so the CO2 is available to all of the plants, plus you will need good maintenance habits, to keep the tank, filter, and water very clean.

How much light you now have depends on whether those bulbs have good reflectors, no reflectors, or something in between, and it depends on having a ballast that drives the bulbs to their rated power. Then it depends on how high above the substrate the light is.

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post #6 of 6 (permalink) Old 01-22-2013, 04:29 AM
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pH/KH combo will give the HIGHEST possible CO2 ppm under ideal conditions, but it typically over estimates ACTUAL CO2 measurements.

So we often think we have more, sometimes a LOT more than we really actually do.

This situation is NEVER reversed, eg, we have a lot more CO2 than we think we do using the pH KH chart.

I use it as a starting place, but then slowly adjust CO2 up little by little, this is very hard/impossible for most aquarist with DIY.

I used many small DIY bottles in series to do that.
PITA, buy a canned gas tank full of CO2, do it right.

Tom Barr
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