# Sticky  CO2,Kh and Ph



## Pterogho

Since questions about CO2, Ph and Kh constantly pop up, I have choosen to give out a deeper going explanation of the relation between these subjects.

It is hardly new to anyone that Carbon plays a critical life-sustaining role to all higher plants.
Plants on dry land rely entirely on the CO2 in the atmosphere to fulfill their need for carbon, while submersive plants in contrast, put further anorganic carbon-bindings in the water to use. That be, in all, CO2(carbondioxide), H2CO3(carbonic acid),HCO3-(hydrogencarbonate), CO3(2)-(carbonate-ion), Ca(HCO3)2(calciumhydrogencarbonate).

Numerous tests and observations in natural biotopes, indicates that most aquatic plants live in slightly acidic waters, with very low levels of calcium and sodium, that also contain sufficient amounts of free CO2 and H2CO3.
Though many plants are adabtable, within certain limits, and hold a quite wide Ph-tolerance, they still seem to prefer the somewhat acidic and soft waters.
Only a small number of plants inhabit calcium-rich waters with a alkalic Ph. These plants are known to be able to utilize, apart from CO2, the availble calciumhydrogencarbonate, at a state of very high photosynthezising.

Photosynthezising plants primarialy need CO2, that forms carbonic acid in water (CO2 + H2O = H2CO3).
At lower Ph values free CO2 and H2CO3 is generally available at sufficient amounts, but if the plants through assimilation take all the CO2 from the water, a rise in Ph will be seen.
Once all the free CO2 is absorbed, different plants respond differently.
While some simply will stop growing, other plants are, more or less, capable of assimilate and use the HCO3- , which will bring the ph even higher, resulting in a solidification of Calciumcarbonate (CaCO3), this will show as calcium build-up on the leaves of these plants.
In fact, scientific experiments have shown that the assimilation of HCO3 can bring the Ph all the way up to 11.
For other plants that rely entirely on free CO2, and aren't able to assimilate HCO3- well enough to support their need for carbon, a way of insuring enough free CO2 ready for them, can prove essential to a keeping of these.
If a consequence can be drawn from this, it must be that it is of outmost importance always to keep the Ph of a planted tank, also if it is just a few plants, that you happen to care for, within a range that will support the highest number plants with different preferences. Such Ph-value would be around 6.2 to 7.2.

Strongly assimilating plants absorb a huge quantity of CO2, and it is ofcause essential to see to, that this important nutrient is present at sufficient levels, while insuring that the Ph is in the above mentioned range, where the CO2 is free for the plants to utilize.

But !!!!
Hold your horses!
Don't go ruin youselves on costly CO2-fertilization-gadgets, unless your tank is very heavily planted, and strongly lighted, and the total CO2-consumption exceeds what the fish and oxidation-processes can keep up with.
Whether or not your plants are without enough CO2, can as mentioned, be detected by the calcium build on leaves, and at times decor, of the tank, and short interval Ph-testing will show a rising Ph, indicating a need of external CO2-supply.
In connection to this it must also be warned that carbondioxide in high concentrations is poisionous to fish, and that there a fish that in no way tolerate low Ph-levels.
So testing the CO2-levels in your tank, along with the other test that are done on a regular basis, is therefore absolutely recommendable.

Still! It gets trickier than all this.
Because prober care of aquatic plants, is not based only on knowledge of the relation between Ph and the CO2-concentration of the water, also the carbonate hardness is a major factor in relation to CO2.
The higher the Kh the more CO2 is needed to lower the Ph, and to keep the calciumhydrogencarbonate dissolved or, in other words, avoiding a build-up of calcium in the tank.
It is therefore, not only economically, sane, to lower the mostly high carbonate hardness of the tapwater, as this is the is the source most of us get our tank-water from.

Test and experiments have shown that an ideal Kh for plant-keeping is between 2 dH and 8 dH, personally I prefer to keep the Kh no lower than 5 dH, as the Ph-stability may decrease substantially below this point.
Water with a Kh of 15 dH and higher does rarely present ideal conditions for the care of plants, as the high buffering capacity makes it difficult, almost impossible, to regulate the Ph.

So. What's the point of all this.
Well! Is your Kh high, your Ph is un-manageable.
Is your Ph high, CO2 and H2CO3 is not fully availble to your plants.
Is the CO2 level high, it may kill your fish, but if it's low, your Ph may go Gung-Ho.
But most of all, if these things are not in place, you fish may have to without O2.








More on O2 in another thread.


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## Husky_Jim

Nice post man!









It deserves to be pinned....


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## sharpteeth

WOW information overload!


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## elTwitcho

Great post, and it's actually easier to get into a situation of rising ph than people realize. I was running 3 wpg and no CO2 on my rhom tank that only had two medium sized hygrophila, some anubia and crypts and some vals and the ph rose on my a good deal during one day of lighting. I ended up adding some DIY CO2 as a result.


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## plantbrain

I'll add to what's be said thus far:

http://faq.thekrib.com/plant-qa.html#co2

While old and some parts outdated, it's still good for the CO2 parts.

Paul is great:
http://fins.actwin.com/aquatic-plants/mont...1/msg00220.html

The point about higher KH is that it provides better protection against
big pH reductions caused by the addition of _strong_ acids, e.g., nitric
from oxidation of fish waste ammonia (not too great a problem in many
planted tanks). KH 1 is fine for stability with H2CO3, but KH 0.001 is
not, and it takes less HNO3 to get there from KH 1 than from KH 3.
Adding strong acids destroys KH.
How you can get and have 0.001 KH is quite another matter! Not practical nor easy by any means using RO and DI. Few test kits can measure this low also, I think there are few, namely Hach's digital tritration kit, about 200$. Yes, I have one because I'm a nerd.

Doubling the KH increases the pH by 0.3 (for the same CO2 concentration),
but does not make it more stable if the CO2 concentration changes.

While no tank or plant requires CO2 enrichment, the trade off for adding it means you have about 10-20X more plant growth! Terrestrial and farm plants also benefit greatly and grow much faster with added CO2 as well, but not to the same extent as aquatic plants.

It really becomes an issue of rate.
More light = more CO2 demand. If you have lower light, then there's not much CO2 demand.
Some plants are very good at living on muhc less CO2 than other species also. Some when folks say they do not need CO2 and that their plants grow like weeds, it may well be true but it'll be in a tank with lower light and the species will be more common faster easy to grow weeds.

pH/KH seems to mess with people a lot.
Some want to use acid "buffers" to lower pH and think this way they can get the CO2 via the pH/KH/CO2 chart. Acid "buffers" are not CO2, plants want CO2, not acid buffers.
If you need more CO2, well..........add more of that. Sounds simple and it is, but many think they can manipulate CO2 with other things like acid buffers.

KH: I've yet to see a single issue with a low KH, I've routine gone to below 0.5 KH with out ever an issue.
Why?
The CO2 rate coming into the tank is still steady, while I may have more trouble measuring the CO2 as the KH approaches zero, as long as the rate of CO2 added, the rate of uptake by the plants remains constant, this matters not.

http://www.aquatic-plants.org/articles/khp...khph_table.html

The tank with a KH = 0.5 and pH 6.0 and a CO2 of 15ppm.

Likewise, the same tank with a KH of 10 and a pH of 7.2 has the same CO2 level.
The difference?
Just KH.

A tank with low KH without CO2 will have a lower pH and a tank with higher KH will also have a higher pH.
We use this table to measure CO2.

Simple enough.

This table makes some assumptions that can get some folks into trouble however.
It assumes that the alkalinity(the same thing here as KH) is all bicarbonate alkalinity and that there are no tannins or other acid "buffers" present.
So pure H2O+ baking soda for the KH.

Some tap water has non carbonate alkalinity, some folks have acids in their water also.
This can cause massive errors in the readings.

High KH's have little influence on plant growth however, a few species are high KH sensitive, about 10-12 species. Most do as well if not better in many cases, but there are few that do certainly better in softer water. Overall, the lower the KH, the better, but it's far from optimal and required in most cases.

GH: these are just the Ca and Mg, both plant nutrients and higher levels, say up to 10-12 degrees have not been found to be detrimental to fish/plants etc of any species I've ever kept.
I keep lots of wild soft water fishes and have for decades.

Since they are nutrients, you will want a fair amount of these.

Folks get most confused when they talk about hardness, total hardness, temporary hardness, carbonate hardness etc.

Best the learn what alkalinity is and general hardness(Ca++ and Mg++).
Stick with those as they are all you really need to know for both fish and plants.
It'll be a lot less confusing.

You can use TDS, EC and salinity etc still for general uses(RO water purity etc).
But Alkalinity and General Hardness as CaCO3 are both parts of the hardness issue and one is a plant nutrient(Ca/Mg) while the other controls the buffering/pH.

Some good background of Alk and GH can be found at www.thekrib.com and older post on the APD.

Plants really do not care about pH or KH, they care about good CO2 levels that are stable.
They will adapt to low non CO2 enriched tanks if you balance the fish loads well with a high plant biomass(not easy with large hungry Piranhas!! unless you do automated water changes/semi automated) or to use CO2 and have a much higher uptake and export of that high fish load and waste production.

You can do as many water changes are you wish using CO2, likelwise the same is true if you do daily water changes using an automated system.

But if you adhere to a non CO2 method, then trying to avoid water changes is the name of the game, so you have to balance what you add, with the plant's growth rates and demands, which are 10-20X slower than with CO2.

Few folks are willing to do that with Discus, Altums, Piranha etc.
So they use CO2.
Hope this helps.

CO2 discussion alone can go for 50 pages alone here. So look around if you have more questions.
One simple method to measure CO2 is the pH/KH reference drop checker and this gets around any non carbonate alkalinity errors form tap water of from tannins etc.

Vaughn has been very promotional about their usage and they have resolved many folk's issues and reduced the testing etc required. 
http://www.barrreport.com/articles/2661-dr...rs-why-how.html

Review this stuff, it'll help you in the long run.
CO2 is the most under rated and over looked part of aquatic horticulture and also the source of nearly 95% of all algae related issues I've ever helped folks with over the years.

Regards, 
Tom Barr


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## pirayaman

this is the most intelligant post i have ever seen but it also has one thing many do not it explains things in a easy to understand way while managing to be severly techinical wow great work you just explained co2 ph kh gh plants fish and water to me and i havent got it for 5 years man thats a good read a must for everybody


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