KH is carbonate hardness, the K comes from the German word Karbonaat. A concentration of 0,179 mmol / l is 1 KH, and if it is double, the hardness is 2. That is, the scale is linear, contrarily to pH.
KH measures carbonate and bicarbonate. Chemically, these are CO3-- and HCO3-.
If I take pure water, and dissolve a bit of NaHCO3, I will notice two things: 1 the KH raises and 2 the pH raises. Further the concentration of CO2 will raise.
pH is a measure of the concentration H+, the agent of acidity. adding H+ lowers the pH, remouving is raises it. Adding HCO3- results in the following reactioin: H+ + HCO3- gives H2CO3, which can fall back, or fall apart into H2O, water and CO2, carbonacid.
As said, KH measures HCO3- and CO3--, and as part of the added HCO3- is turned into CO2, the raise in KH is not what one had expected.
If one waits, the tank, which is in equilibrium with a certain pH, will lower the pH, which results in more H+ in the water. This will react further, and in the end (allmost) all HCO3- has been turned into CO2.
However, if one keeps adding HCO3- to the water, the tank will lose, and the pH (and KH) will raise.
Still, this can also happen the other way around - adding CO2 will in the end lower the pH and also raise the KH.
Air does contain CO2, which readyly dissolves. Under current circumstances, water, in contact with air is in equilibrium when it contains 5 mg CO2 a liter. Depending on the pH this will react with H+ to form HCO3- and CO3--, that is KH
Around pH = 5, with this CO2 concentration the KH is low, less than 4, but with higher pH, the KH can be much higher.
How can one reach such a high KH? Easily, by keeping the water moving. In the end, the plants will get enough CO2, so the water can reach equilibrium, that is, reach the natural KH.
Many plant keeping people say moving water remouves CO2 from the water, but that is not the case. Moving the water will help reaching equilibrium, that is 5 mg CO2. But many plant keeping people think the plants need more than this 5 mg CO2, so they aim for much higher, sometimes as high as 25 mg. A pity, because these concentrations of CO2 will result in higher concentrations of this stuff in the fish, which is harmfull.
But, back to my point, if your KH is less than 4, and the pH is not 5 or less, the problem is easily solved by moving the water
CO2 + H2O gives an instable molecule, H2CO3. This molecule can fall apart in two directions, it can fall back, H2O and CO2 or it can fall into H+ and HCO3-
That is, increasing CO2 in the water wil lincrease both the concventrations HCO3/, that is the KH and H+ - that is lower the pH.
hope this helps
I wonder what there is to disagre about
On one hand, KH does not measure CO2. That is true. But, after adding CO2 to water - any water, unless too low a pH - the KH will raise.
Not fully, that is, if you add 0,179 mmol CO2 to a liter water, the KH will NOT increase by 1, but less. That is because part of the CO2 will notturn into HCO3- and therefore not be measured as KH
But around pH = 7, around 0.1 part (or 10 %) of the CO2 will turn into HCO3-, and around pH = 9 it will be quite closte to 99 %.
HOWEVER, if you have a tank with lots of plants, few fishes, most likely the amount of CO2 in the tank is less than equilibrium. And thus, if you add CO2, the plants will take it, resulting in no measurable effect. In pH, KH or whatever
I think you're providing false information. The KH is not affected by the addition of CO2...Read more on the subject. I am not squeezing this out of my fingers....Its a proven fact.On one hand, KH does not measure CO2. That is true. But, after adding CO2 to water - any water, unless too low a pH - the KH will raise
P.S. Let me rephrase myself in order to be factually correct. The effect of CO2 on KH is so little, that can be completely ignored.
I don’t know what to make of all of this but I did find this article. I have zero live plants and basic old lighting.
I have gotten KH to 2 and PH when I checked last was 7.6. I bet it will be lower when I check later this morning. If it’s between 6.8-7.2, how safe is this for fish? (Checked this morning. 7.6). I looked at the chart in the article. I’m still not 100% sure what is safe. Again, I run two HOB filters that provide surface agitation and a bubble wand. The fish don’t appear to be stressed. No gasping, no surface hanging, no lethargy.
How important is buying new lighting? I have no live plants. I’m reluctant to spend more money on equipment on this tank because within the next 3-6 months I will be purchasing a minimum of an 100 gallon tank. If I get an acrylic I can’t use my HOB filters. And I don’t want built in filters because it takes away water volume for fish. I’m not a fan of canisters either but I prob won’t have a choice.
I’m taking in everything everyone is saying and appreciate all the input.
Nitric acids, humic acids and other organic matter will all contribute to acidification of aquarium water. This will typically result in pH readings lower than the table assumes — resulting in a false CO2 calculation.
what made the pH low does not matter as CO2 and H+, regardless their source, just react with each other
But, what irritates me more, is the assumption that 30 mg/l CO2 is safe. It is not. If I put my hands on someone´s throat and squeeze slightly, he will not die, he just has a little problem breathing. A bit uncomfortable. Obviously, I would be quilty of mistreating the person, and should go to jail for a long, long time.
Adding CO2 to the water makes it for the fish harder to get rid of the CO2 in their body. They will not die, but be uncomfortable. Just as the person in the example I provided.
Fish, having a central nervous system, can be uncomfortable. Plants, without such a system, cannot. This makes sense, fish being in unhealthy places should swim away, but plants cannot move.
Therefore one should not add CO2 to water where fish are swimming. But when I had a planted tank, without any fish (they were ordered, but not delivered yet) I added a little NaHCO3 to the water every day. The day I got the fish, I changed 80 % of the water (I knew this stuff had made the pH higher than needed) and thus the fish never had any trouble with what I had done.
With regard to your water, a pH in the morning is most often lower than in the evening, due to plantgrowth. A tank without plants most often has algae, doing the same. Whether a pH is safe depends o nthe fish. a pH of 7.6 is not suitable, too high, for Discus, obviously, but also dangerously low for Lake Malawi fish.
Finally, in a tank without any fish, I would replace the TL only if it stopped working. Not a day earlier.
Great news about purchasing a 100G tank Fran. The bigger, the better so see if you could squeeze even larger In the end though, is all one can do...so no worries. Have you considered an indoor pond? I got one the last time I was in extreme hurry after my clown loach tank broke and funds were not in abundance at that moment of my life....I can show you some pictures if you're interested. Its been running for less than 1.5 years.I have gotten KH to 2 and PH when I checked last was 7.6. I bet it will be lower when I check later this morning. If it’s between 6.8-7.2, how safe is this for fish? (Checked this morning. 7.6). I looked at the chart in the article. I’m still not 100% sure what is safe. Again, I run two HOB filters that provide surface agitation and a bubble wand. The fish don’t appear to be stressed. No gasping, no surface hanging, no lethargy.
Do not fret about pH!!! It is the TDS that causes osmotic shock or osmotic intolerance, and extreme pH drops simply because the levels of acids are too extreme for the fish to handle. pH on the rise, and pH values between 6 and 8 are fine for all fish. Your water still remains soft, i.e your TDS levels. That's all your fish know and understand.... Now it is a different story if your water had a wide jump in pH due to a very fast rising TDS!!! pH is an indication of "something happenign", but it is the underlying factors that should be considered to decide if it will affect fish or not. In some instances they do, in others they totally don't, such as the CO2 injection(with that difference CO2 is toxic to fish). In your case, all you're adding is baking soda, so water chemistry is unaltered.....Fish should not care one bit, should be better for it as the pH should become stable and should never dip in and out of intolerable levels as long as there's some Kh reading.
I totally agree. CO2 is toxic to fish, more so to certain species than others, but in general it is poison...Although, on a very low level, fish, and even humans require CO2 for natural well being, which is just enough in a low tech tank. Same applies to shrimp. Copper is toxic to them but it is also essential for their well being, in extremely tiny amounts...But, what irritates me more, is the assumption that 30 mg/l CO2 is safe.
Oh, how I love people boasting about their education.......Yours stopped in 1992. Mine is still ongoing...I graduated in Chemistry in 1992. When did you?
"Education is what remains after one has forgotten what one has learned in school"
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