# Low light + CO2 - Dosing amounts



## JohnC (26 Feb 2012)

Hi,

I'm going to do a low light tank with CO2 and some nutrient heavy substrate ive got kicking about spare.

My aim is really to see what I can grow at lower light then to see how much I can reduce my maintance by but I am wondering how much I should expect to need to reduce my dosing by?

Most of the information I read on low light set ups work on no additional CO2. 

Am I safe to assume that with heavy root feeders like Crypts i'm planning on using, and low demand mosses + my fish load I'll be fine without adding any water column dosing? Or just target certain nutrients?

As I mentioned earlier since I'm adding CO2 I expect its level should remain stable and I'll keep doing weekly water changes (which make me happy as well as my fishes). 

My question is really about what level of reduction from high energy EI levels of nutrient dosing to low energy should I be expecting to do? 100%, 50%, 25%?

Your experiences to give me a gauge on a starting point welcomed.

Best Regards,
John


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## foxfish (27 Feb 2012)

I am not sure what you are tying to achieve?
Why not a low tech tank without injected C02?

Plantbrain recently wrote ....

"Adding CO2 will lower the threshold of the LCP(light compensation Point where PS = R), so contrary to belief, CO2 allows you to add even LESS light, than non CO2. This is because all the resources the plant takes in and uses can be geared towards capturing light instead of capturing light AND limited CO2."

I am using 70w over approx 200l & every thing is growing well.


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## Antipofish (27 Feb 2012)

foxfish said:
			
		

> I am not sure what you are tying to achieve?
> Why not a low tech tank without injected C02?
> 
> Plantbrain recently wrote ....
> ...



Does what Tom wrote above not just mean that CO2 works fine with a low light system ?  Essentially, turn that around, and it means that using CO2 on a low light system will enable better growth because the plant can utilise what light there is better right ?  Or am I being daft. LOL.


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## ceg4048 (27 Feb 2012)

JohnC said:
			
		

> Hi,
> 
> I'm going to do a low light tank with CO2 and some nutrient heavy substrate ive got kicking about spare.
> 
> ...


Hello,
    As foxfish mentions, it's really not clear what it is that you're after. On the one hand you're saying that you're not as much interested in lowering maintenance, yet you seem focused on reducing the dosing - which is done primarily to reduce maintenance, and secondarily to lower TDS.

Just because you lower light this does not automatically mean that you are compelled to lower the dosing, but it does mean that you may lower the dosing.

In any case there is no way anyone could possibly predict what reduction in the dosing levels any tank can take because no one knows the flow, or the actual CO2 levels, or the actual lighting, or the fish load or a score of other factors that determine uptake rates and productivity, so you yourself will have to determine that by incrementally lowering the dosing. Start by an arbitrary 10%, wait a few weeks and then if there are no issues, reduce by another 10% and take a reading in another few weeks. Continue until signs of distress are noted.

So-called heavy root feeders take as much or more nutrition from the water column as any other plant and non-root feeders take from the substrate just as well except for those plants that do not send roots to the substrate.

Cheers,


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## JohnC (28 Feb 2012)

ceg4048 said:
			
		

> Hello,
> As foxfish mentions, it's really not clear what it is that you're after. On the one hand you're saying that you're not as much interested in lowering maintenance, yet you seem focused on reducing the dosing - which is done primarily to reduce maintenance, and secondarily to lower TDS.
> 
> Just because you lower light this does not automatically mean that you are compelled to lower the dosing, but it does mean that you may lower the dosing.
> ...



You have kinda hit it on the head there.

Primarily i'm trying to see what I can grow under this single low light LED setup i'm making (i can do a PAR reading later). 

I want light as my only limiting factor with no worry that CO2 will bottom out or end up fluctuating with water changes. 

The Tom quote that Foxfish writes is interesting as I was wanting to see which of my higher energy plants could cope with this regime. 



> Plantbrain recently wrote ....
> 
> "Adding CO2 will lower the threshold of the LCP(light compensation Point where PS = R), so contrary to belief, CO2 allows you to add even LESS light, than non CO2. This is because all the resources the plant takes in and uses can be geared towards capturing light instead of capturing light AND limited CO2."



I'd be happy to start by using my full EI dosing schedule but i'm aware that is more then i'll actually need. 

I was really fishing around to see if people have observed/tested a very rough rule of differential % absorption of dosed nutrients under the different intensities of light. Where for example Tom has tested the maximum absorption of plants under "unlimited light" is there a graph or scale of the way that drops off under decreasing light in the same tank? 

Thus even though, as you mention, the individual variables of my new set up will obviously end up dictating my actual nutrient consumption I could be confident that I could make up solutions at the start of say 30% or 40% weaker then the norm and skip the slow decrease in dosing over weeks and distressing the plants and inducing algae. This while carrying on larger water changes.

You see what I mean?

Best Regards,
John


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## ceg4048 (28 Feb 2012)

JohnC said:
			
		

> ...I was really fishing around to see if people have observed/tested a very rough rule of differential % absorption of dosed nutrients under the different intensities of light. Where for example Tom has tested the maximum absorption of plants under "unlimited light" is there a graph or scale of the way that drops off under decreasing light in the same tank?


It would be extremely difficult to determine this because the relationship between uptake and other variables is non-linear. Generally, the more you dose the more the plant will uptake, and this is true of any lighting level. One would then have to set the PAR level and CO2 level then continue to add higher levels nutrients until no more higher growth rates were observed. You would then generate a graph that would have different nutrient levels as saturation points as a function of PAR and CO2. Since each plant is different there would be different plots for different species. The fact that uptake rates increase with increased concentration makes it very difficult to ascertain these values easily. I've tried this by increasing the values up to 3X-4X EI values and growth rates simply went over the top.
Also, there is coupling between nutrient levels and CO2 because, for example Nitrogen assimilation is dependent on carbohydrate levels and carbohydrate production is a function of Nitrogen availability. Very difficult to untangle the thread...


			
				JohnC said:
			
		

> I'd be happy to start by using my full EI dosing schedule but i'm aware that is more then I'll actually need.


Well, yes, this is true, but that's the methodology of a eutrophic dosing system anyway.


			
				JohnC said:
			
		

> Thus even though, as you mention, the individual variables of my new set up will obviously end up dictating my actual nutrient consumption I could be confident that I could make up solutions at the start of say 30% or 40% weaker then the norm and skip the slow decrease in dosing over weeks and distressing the plants and inducing algae. This while carrying on larger water changes.
> 
> You see what I mean?


Yep, if that works then you'll be saving 30% to 40% on cost as well, so this is significant if dosing a big tank certainly, but as I mentioned, you might not learn what you thought you would learn. I'm of the mindset to see what happens at both dosing end points, high as well as low....

Cheers,


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## JohnC (28 Feb 2012)

Very wise advice, as ever. 

Thank you very much for taking the time to respond.

Best Regards,
John


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