# New and asking the usual CO2 question - help?



## Akilia (Apr 8, 2006)

Hi,
I've got the usual question, does my tank need CO2 and if so, what is the system setup recommended. I do not want a DIY CO2 setup.

My local water is ground source:
pH 7.4, 8 deg dKH, 14 deg dGH, Ca 84mg/L, NO3 34ppm, NO2 0, Fe 7ppm.

When mixed 50:50 with my rainwater it yields:
pH 6.8, 5 deg dKH, 7 deg dGH, NO3 15ppm, NO2 0ppm.

I propose an Amazonian planting scheme maintaining cardinals, an algae-eating Peckdoltia, and 2 discus, plus a few corydorus.

My planting scheme includes:
Rear/Side height:
Alternathera reineckii (4)
Myriophyllum elatinoides (2)
Mayaca fluviatilis (2 or 3)
Hydrocotyle leucocephala (3 or 4)
Mid-ground structure:
Heteranthera zosteraefolia (1-2)
Echinodorus osiris (2)
Lower cover:
left: Echinodorus tenellus (10)
mid-right: Echinodorus latifolius (3)
right: Lilaeopsis novae zelandiae (4) (yes yes kiwi I know, but its brill)

I might put one or two ferny plants on crevices in one of my bogwood pieces, depending on what suitable plant specimens I find (any suggstions within the biotope theme?).

According to pH/KH : CO2 tables, there will be approx. 20ppm CO2 in my water if I mix 50:50, and about 30ppm if I mix 60 RW:40 TW. Of course the exact mix depends on the effect of the aquasoil and bogwood on water parameters, but it will be around 20-35ppm CO2 surely?

Do I need CO2??
If so, what low-maintenance delivery system would u recommend and how would it be rigged?


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## Bert H (Mar 2, 2004)

Hey Akilia,

Welcome to apc! Let me try to address a couple of points you bring up. The amount of CO2 in an equilibrated water sample is debatable, but for arguement's sake we can say around 3ppm. Your sample is artificially affected by your rain water, I am guessing either you are seeing the effects of some 'acid' rain or your collection apparatus is affecting the pH acidically somehow. Therefore correlating your KH/pH/CO2 is going to be problematic. 

Your tap water doesn't sound too bad to me. Are you sure about your nitrate readings? 30+ppm NO3 is a little high, but workable, you'd never have to dose it! I would suggest you run a standard with your nitrate kit to verify the readings. What are your phosphates? 

The question of CO2 or not deals heavily with how much lighting you have. I don't see where you mention that. If you have high lighting, you need CO2. At lower levels and on smaller tanks you could get away with Excel, or going low tech with no carbon supplementaion. Some of the plants you mention will require decent lighting, and CO2 will be beneficial in that respect.

HTH, and again, welcome to apc.


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## Akilia (Apr 8, 2006)

Thanks for the welcome 
I put my tank data in my sig.
I have checked my water parameters using API liquid kit and LFS confirm. I've been monitoring them for a couple of weeks, consistent results.
My tap water alone is not suitable for my planned fish and plant scheme, water changes will be too alkaline, too hard, and too much nitrate hit for the discus. I have to mix it with RO water or rain water if i'm going to get them to breed.
Even 17ppm is too much nitrate for my liking, but will be useful for the plants. If they thrive, the nitrates should fall nicely.

The Juwel lights were awfully dull and grey.
I chose Interpet Daylight Plus 25W, because I didn't want to change to the Arcadia I-Bar T5, and that was the brightest triphosphor T8 tube I could find which was balanced for planting and it gives a good colour with the Arcadia Tropical 25W, my other tube, when I saw it in the nearly-LFS. (Obviously there are 50Watts and there 50Watts!!)

I don'y yet know the PO4 reading, and the NO3 IS awfully high, something to do with unrestrained nitrate farm fertilisers and livestock manure leaching I should imagine.

I understand your comments about the pH/KH carts limitations. 
The tap water should be OK for the calculation though?
I imagine the acidic rain (nothing to do with the collection system) is nitric acid mostly, with a little H2SO4. Without knowing the anions I can't really calculate CO2, I'll have to measure it I suppose.

So what delivery system would you recommend?
Lighting-linked?
pH sensor (but the anion question??)

Thanks.


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## Laith (Sep 4, 2004)

If I understand correctly, you have a 180l tank (about 47g) with 50 watts of light over it? 

If that's the case, you're at just over 1 watt per gallon and you are definitely in low light territory and CO2 is not a requirement, though it always helps.

Lowering your KH does not increase CO2 if you're not injecting it. I cannot see how you can have a KH of 4 and a pH of 6.6 without the addition of CO2. Either your pH reading is off or your KH reading is being affected by something in the water. 

At ambient pressure and equilibrium (and with no CO2 injection), at a KH of 4 your pH should be around 7.6.

I think that some of the plants you've listed may struggle to survive in the lighting you have...


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## Akilia (Apr 8, 2006)

OK so this is where I have a problem.

Rainwater here has low pH, below the limit of my testing kit.
My tap water is pH 7.4-7.5, 8 deg dKH, 14 deg dGH, NO3 34ppm. Honest.
My test says it, and severn trent water says it.

I mixed rainwater and tap water 50:50 and 60:40, and tested them.
I measure the water parameters of the tap water, and the two mixtures, using API liquid test kits.

Rainwater is not pure as we all know. It must contain nitric and sulphuric acids in small amounts, the acid rain.
When it is mixed with KH8 tapwater, the strong acids must react with the weak basic buffer (carbonates). This wipes some of the carbonate, liberating CO2 and leaving nitrates and sulphates.
So the strong acid is buffered and the pH adjusts only a little down.
The resulting mixure 50:50 measures as pH 6.8, 5deg dKH, 7 deg GH, NO3 17ppm. Presumably the hardness had fallen simply by dilution.

Why would my measurements be out? Would it be because of "insufficient time for equilibration" so some transient increase in carbonic acid is yet to dissipate or something like that?

I am interested in how one calculates the values you gave. It seems pretty fundamental to my required understanding.

Re: my lighting, yes but I believe that the luminance of the interpet tube is much greater than the luminance of non-triphosphor 25W tubes; certainly there is a huge difference between the Juwel ones and the combination I now have. Though clearly I am not working with high lighting of >2W/gal. 
Which plants am I going to struggle with due to lighting problems?

Thanks for your further thoughts...


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## hoppycalif (Apr 7, 2005)

Alternathera reineckii does not do well without at least moderate lighting, and would be a green plant under the low lighting you are proposing, in my opinion. Mine grew very, very slowly at 1.75 watts per gallon, but grew faster and bigger and redder with 3.8 watts per gallon.
Planted aquaria, in my opinion again, do best if the tank is set up to favor good plant growth, before considering what a specific species of fish prefers. Most, if not all of us have fish or shrimp in our planted tanks, of various species, and they do fine with a variety of water conditions. So, please don't get too carried away trying to match some fish "requirement" that is badly overstated by the LFS.


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