Question about Excel and Lighting - The Planted Tank Forum
 
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post #1 of 10 (permalink) Old 06-19-2012, 03:40 AM Thread Starter
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Question about Excel and Lighting

Hello folks,

From the information I've gathered, it seems that the general consensus is to dose excel right before light goes on for its maximum effectiveness, which doesn't seem to make much sense to me.

I know that photosynthesis is comprised of light reaction and dark reaction, and the dark reaction can go on without the light reaction, assuming that there are enough energy saved during the light reaction in the form of NADPH and ATP.

So basically, the light reaction goes:
Light + H2O + ADP + NADP -> O2 + ATP + NADPH
...which ATP and NADPH are the energy molecules produced.

Then, the energy generated in the form of ATP and NADPH from the light reaction are used during the dark reaction for plant growth:
CO2 (or other carbon source, such as excel) + ATP + NADPH -> glucose + ADP + NADP
...where energy stored in ATP and NADPH are used up to form glucose, and you get ADP and NADP again.

So, in all reality, the light reaction begins when the light turns on, but it will take a while for the plants to produce enough ATP and NADPH. The ATP and NADPH, in turn, are used to produce glucose in the dark reaction along with CO2 (or alternative form of carbon source).

Based on the information above, wouldn't it make more sense to dose excel once the light has turned on for a while? (Say, 1 hour or so) By then, the light reaction would have produced enough ATP and NADPH, which will prime the dark reaction. Then, as soon as you add excel it would be immediately used up, rendering it more effective.

Just my 2 cents!
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post #2 of 10 (permalink) Old 06-19-2012, 03:57 AM
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I think adding CO2 before the light comes on is to make sure it gets a chance to circulate around the tank. But that should only take ten minutes or so, so I guess you're right. CO2 gas would need longer to build up to the desired PPM, but with Excel that's not an issue.

Do you know how long the plants keep using CO2 after the lights turn out?

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post #3 of 10 (permalink) Old 06-19-2012, 12:18 PM
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I'm not sure what type of plants aquarium plants generally are (C3, C4 or CAM), however, I'd guess C4 plants, which means that the reactions are seperated spatially, not temporally, with the dark reactions being deeper within the tissue. The reactions involved in photosynthesis are very fast, so it doesn't take long for them to increase energy levels (plus they store energy). The idea of turning CO2 on a couple of hours before the light turns on is to build up the amount of CO2 in the water, so maximising the amount the plants can take up, as said above, this would mean excel need not be added before the lights are on.
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post #4 of 10 (permalink) Old 06-19-2012, 01:32 PM
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Dosing Liquids and Lighting

Hello j...

Whoa. That was an awesome chemistry like thing you posted. Is lighting and dosing the trace elements that complicated? I'm definitely not an aquatic plant professional, but it seems to me a weekly dose of a good micro nutrient at any time would be sufficient for the plants. My point being, the time isn't as important as dosing on a routine basis.

Since the fish and large, frequent water changes take care of the macro nutrients the plants need, the only thing we need to do is dose the micros regularly. I find it's easiest to dose my liquid fert when I do the water change and that can be whenever time permits, but it should always be dosed weekly. As for the lights, I just have them on timers to come on at 6 A.M. and go off at 6 P.M. Of course I have moderate light and use a couple of T5s, nothing fancy and don't keep demanding plants.

Just a thought.

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post #5 of 10 (permalink) Old 06-20-2012, 02:00 PM
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He's not talking about ferts. He's talking about Excel, which is a CO2 substitute. Plants breathe oxygen in the dark, so there's no need to add Excel when the lights are off. The OP is trying to show us why there is no need to dose Excel before the lights come on, unlike CO2 gas, which requires time to build up to the desired levels in the tank.

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post #6 of 10 (permalink) Old 06-20-2012, 02:58 PM
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Excel & Lighting

Quote:
Originally Posted by Fishly View Post
He's not talking about ferts. He's talking about Excel, which is a CO2 substitute. Plants breathe oxygen in the dark, so there's no need to add Excel when the lights are off. The OP is trying to show us why there is no need to dose Excel before the lights come on, unlike CO2 gas, which requires time to build up to the desired levels in the tank.

Hello F...

Thanks for the information. I'm familiar with Excel and it's contents. It's just interesting to me, the carbon dioxide the fish produce should have the same affect on growing plants, but without the "Gluteraldehyde"(1.5 percent), that the Seachem product has. Excel is apparently toxic to some ferns, mosses and Vallisneria.
Again, just curious why it's being used when there are safer, more natural alternatives.

Again, just a thought.

B

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Last edited by BBradbury; 06-20-2012 at 06:42 PM.
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post #7 of 10 (permalink) Old 06-20-2012, 03:05 PM
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Originally Posted by BBradbury View Post
Since the fish and large, frequent water changes take care of the macro nutrients the plants need, the only thing we need to do is dose the micros regularly.
B
No, not necessarily. It depends on your tank, and especially the intensity of your lighting. You may have great success with low to moderate light tanks that thrive with nothing more than large weekly water changes and minimal dosing --I have several tanks like that myself-- but that advice does not work in all situations. I can only imagine the starving plants and algae farm that would ensue if I tried that on a high light tank!

And as the previous poster pointed out, please note that Excel is not a fert. It is a carbon substitute. Hasn't this been addressed before?

To get back to the original post (uh, sorry about the ranty thread jack ), to be honest, I'd never really given much thought to the timing of Excel dosing. If I dose it before lights come on, it's because that's when I remember to dose the tanks.

I suppose I had some vague notion that dosing Excel before lights came on meant that it was available right away. From what you are saying, though, it sounds like it does not work the way I thought. But is there any reason not to dose before the lights come on, if that is what is easiest? Or are you just pointing out that it's not necessary to time Excel dosing prior to the lights coming on?


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post #8 of 10 (permalink) Old 06-20-2012, 03:41 PM Thread Starter
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Quote:
Originally Posted by chicken View Post
From what you are saying, though, it sounds like it does not work the way I thought. But is there any reason not to dose before the lights come on, if that is what is easiest? Or are you just pointing out that it's not necessary to time Excel dosing prior to the lights coming on?
Because the half life of glutaraldehyde is about 12 hours in an aquarium setting, even if the plants don't consume it. This means that after 12 hours, 50% of excel will have undergone transformation and no longer in it's active form whether plants are present to use it or not.

So, what I am trying to figure out is a way to dose excel most efficiently. If I dose excel 1 hour before the light goes on, then excel sits there for another hour or two before plants actually start using them, I am wasting quite a bit of excel by just letting it sit in aquarium for hours and become inactive.

For example, we know that glutaraldehyde has a half life of 12 hours and it undergoes exponential transformation.
The half life equation goes as follows:
Nt = N0(1/2)^(t/t1/2)
Where
Nt is the amount remaining
N0 is the initial amount
t1/2 is the half life
t is the time elapsed.

And let's assume you dose excel 1 hour before light goes on, and it takes plants about 1 hour to start taking excel up as alternate carbon source.

Plug those numbers into equation, and you get 89% of original amount, before the plants even start using them.

This can definitely be quite wasteful, especially if you have a large aquarium. For instance, an 100 gallon tank dosing excel as recommended will use 10 ml of excel a day. In a month a large aquarium would need about 300 ml of excel. Assuming only 89% efficiency you are practically wasting more than 30 ml of excel away each month. That's a lot excel going to waste!
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post #9 of 10 (permalink) Old 06-20-2012, 05:03 PM
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Originally Posted by jigabodo View Post
Because the half life of glutaraldehyde is about 12 hours in an aquarium setting, even if the plants don't consume it. This means that after 12 hours, 50% of excel will have undergone transformation and no longer in it's active form whether plants are present to use it or not.
Drat. I obviously wasn't thinking about that.

So now I have to decide if I'm going to do this right, or if I'm just going to decide that the imperfectly timed dose of Excel that does happen is better than the perfectly timed dose which doesn't happen.


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post #10 of 10 (permalink) Old 06-20-2012, 09:45 PM
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I have heard many times about the 12 hour half life of Excel in an aquarium. Does anyone know what is happening that causes Excel to break down that way? Suppose I just mix Excel with water in a jug, will it break down the same way? What about medical glutaraldehyde? Does that mean mixing glut with water, to dilute it, starts the breakdown? None of this makes any sense to me.

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