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Why do we aim for 30 ppm CO2?

"On the first one please get out of the chemistry class. This is an aquatic forum and we are discussing aquatic realities, not basic water chemistry."

There's no need to take that tone. This is an aquatic forum. By definition, water chemistry is a huge part of our hobby. It is one of the most important things we should discuss. I don't understand why you've taken issue with it. I misunderstood your post is all. It seemed like you thought that the KH and pH are completely unrelated. Obviously I was mistaken, so it's just a failure to communicate, no disagreement as such. Sorry if I've been at all confrontational
 
Secondly, you say that my second statement is quite incorrect? In what way exactly? Are you trying to say that changes in pH caused by Co2 give the fish Osmoregulatory difficulties?

Yes if the PH changes caused by CO2 are big enough.

Sorry mate, this is definitely not true. There are zero osmoregulatory effects of pH changes due to CO2. Fauna will perish due to CO2 toxicity long before they are affected by pH. Carbonic acid is a very weak acid and does not produce enough free H+ to make a difference in the Na+:H+ exchange mechanism. In any case I can have (and have done) as much of a pH drop as I want without any issues. I specifically controlled the pH drop by a combination of varying the alkalinity and varying the CO2 content until the pH exhibited extreme drops. Fish bred in this water with a pH drop of approximately 5 units (pH 7-> pH 2) which is approximately 100,000X increase in acidity. So the answer, at least as far as S.A Dwarf chiclids, common Tetras and Discus are concerned, is.....No.

Cheers,
 
Sorry mate, this is definitely not true. There are zero osmoregulatory effects of pH changes due to CO2. Fauna will perish due to CO2 toxicity long before they are affected by pH. Carbonic acid is a very weak acid and does not produce enough free H+ to make a difference in the Na+:H+ exchange mechanism. In any case I can have (and have done) as much of a pH drop as I want without any issues. I specifically controlled the pH drop by a combination of varying the alkalinity and varying the CO2 content until the pH exhibited extreme drops. Fish bred in this water with a pH drop of approximately 5 units (pH 7-> pH 2) which is approximately 100,000X increase in acidity. So the answer, at least as far as S.A Dwarf chiclids, common Tetras and Discus are concerned, is.....No.

Cheers,
Interesting. We are talking about sudden PH fluctuations meaning as much as drop and raise as well, not just in one direction.
I have seen how fish get severely startled with this changes either hiding in corners or going top side (when CO2 is too much).
What do you think is causing that taking the TDS does not change?
I am talking about a case where the GH and KH a very high and CO2 regulates the PH down. So if CO2 stopes for any reason PH will shoot up by a lot within an hour. This is a case with many folks here that are running on tap water which is too hard and growing plants gets a bit difficult.
In one case CO2 concentration is too high, PH goes very low, but I would say it is the CO2 that's causing the trouble. So that's clear issue.
What happens if the water gets relatively fast at high PH levels let say from 5 to 15?
And then again.
What's the relevance of TDS in this discussion if this parameter have to be stable in the first place and one does not move fish from one tank to another all day long? I have never seen TDS changes in my tanks unless I use a lot of fertilisers or let the water evaporate half way.
The only case when I had TDS changes were when I experimented with Calcite rocks in CO2 enriched aquarium and yet TDS were not changing any near fast enough to cause any problems to fish.

Yes Clive your theory is beyond question correct, but we are not moving fish all the time and aquariums are usually stable in TDS reading are they not?

If we want to say what else would get fish in osmoregulatory trouble that would be sudden shift in temperature for example and is not even TDS related, but then again it will be a man made reason, not something that would ever occur in a stable environment.

So I suggest we stop biting on the letter and get the tanks stable and then see what happens with the osmoregulatory functions of fish.:)
 
Aquadream,

what you need to realise is that pH is an arbitrary and pretty meaningless measurement. It is not a measurement of anything chemically tangible, but rather it is a mathematical procedure, referred to as a "chemical speciation calculation". This is the function used to calculate pH:

pH = -log aH+

aH+ is Hydrogen ion activity. The important thing to note here is that pH does not measure the true concentration of hydrogen. It measures the effective concentration. This is because it must account for the fact that other ions around the H+ ions affect their ability to participate in chemical reactions, basically changing the hydrogen ion concentration in any process that involves H+.

pH gives a rough overview of all the chemicals present in a solution that contribute to acidity or alkalinity, it can't tell you anything specific.

An obvious analogy is TDS. TDS doesn't actually mean anything at all. TDS is (sort of) another chemical speciation calculation, insofar as it takes a reading (conductivity) and applies a mathematical function to it to obtain a different reading.

Now, what does total dissolved solids actually tell us? Nothing. It tells us roughly how much "solid" is dissolved in the water. But what is that solid? It might consist entirely of potassium bicarbonate, in which case the fish won't care, but it might consist entirely of chloramine and ammonia, in which case the fish will die. So two identical measurements of TDS (for argument's sake let's say 100 and 100) look identical, but can be the difference between life and death. This is because it is an overview of everything in the water.

Back to pH, it is exactly the same story. It gives a rough outline of everything present in the water. Let's take a theoretical swing of pH from 7.0 to 6.0. Now what has actually changed to cause this reading? The power of hydrogen is what has changed. What does that even mean, power of hydrogen?

What Clive said here is the crux of the issue:

Carbonic acid is a very weak acid and does not produce enough free H+ to make a difference in the Na+:H+ exchange mechanism.

The fish don't care about the pH changing. They care about whatever happened to cause the pH to change. If the pH change was caused by a significant change in the exchange mechanism, then it changes the chemical capability of the water. The water will behave in a different way in relation to other chemicals.
If the pH change was caused by dissolution of a very weak acid, the chemical composition of the water remains basically the same. The dissolved acid is too weak to change the way in which the water behaves in relation to other chemicals. All the chemical processes/ reactions that happen will be virtually unaffected by the extra acid, and will remain pretty much the same.

I hope I've made this clear as it's a long time since I studied this. If there are any mistakes in what I've said I'm sure Clive will pick up on them.
 
Interesting. We are talking about sudden PH fluctuations meaning as much as drop and raise as well, not just in one direction.
I have seen how fish get severely startled with this changes either hiding in corners or going top side (when CO2 is too much).
What do you think is causing that taking the TDS does not change?
It's exactly as Sacha explains. The toxicity of CO2 has to do with the dissolved gas pressure in the water which makes it difficult for the fish to exhale. Imagine if I put a plastic bag over your head and forced you to re-breathe the air you exhale. Any living thing that consumes carbohydrates, and which burn the carbohydrates with Oxygen will always produce CO2 which has to be eliminated from their system. Within the bloodstream, the Carbonic acid that results from the tissue produced CO2 changes the pH of the blood and that acidity inhibits the Oxygen carrying ability of red blood cells. We and fish have to expel the CO2 or suffer hypoxia. High CO2 pressure in the water column pushes back against the fishes attempt to push CO2 out through the gills.

It isn't necessary to have a large pH drop to have this happen. In high KH water, if you inject too much CO2 the fish will suffocate just as easily, but the pH drop will be very small. So the fish are responding to the high dissolved CO2, NOT to the pH drop. I think this is one of the key misunderstandings in the hobby. Fish do not care about pH or pH fluctuations, large or small. As Sacha quite rightly points out, fauna care only WHY the pH has fallen or risen. If the pH falls or rises due to a toxic agent, then they will be affected by the toxic agent, not by the pH change.

Regarding your hypothetical question of what happens if the pH rises from 5 to 15, remember that it's very difficult to separate the analysis of all the different agents in water because each factor has an effect on the other. So in order to answer this question, you'll need to specify exactly what agent caused the pH to rise. What are the initial conditions? The answer to those questions will tell you how the fish will respond. It's very difficult to raise the pH of the water from 5 to 15 except by the addition of caustic alkaline substances such as Sodium Hydroxide to the water. Sodium Hydroxide is a toxic substance and is the principle ingredient of Oven Cleaner or Drain Cleaner. So, if that is the agent being used to raise the pH then we can confidently predict that it will annihilate the fish. A more reasonable hypothetical would be to raise the pH say, from 3 to 8. That's easy to do by simply adding some salt of Carbonate, such as Sodium Bicarbonate or Potassium Bicarbonate. That will neutralize the acid in the water and will raise the alkalinity. The fish will not be affected. Another hypothetical situation is one in which the initial pH is 5 and large doses of ammonium (NH4+) is added to the water. At a pH of 5 the NH4+ <=> NH3 equilibrium is shifted mostly to the less toxic NH4+. If we now add copious amounts of any Carbonate salt to raise the pH above 7, the equilibrium will shift to the right and there will suddenly by highly toxic NH3, which will also annihilate the fish. As I mentioned before, it's very easy to drop the pH with low KH and small additions of CO2. But suppose I dropped the pH with Hydrochloric Acid and high KH water instead of using Carbonic acid? Well, yes a drop from 7 to 5 in high KH water indicates that large amounts of caustic acid has dissolved in the water and yes, this also completely annihilate the fish.

Each scenario has to be analyzed within the context of the original conditions and the agents responsible for the change of pH. To only look at the pH change itself without context is not meaningful and it is often what causes people more grief. When there is too much CO2 dissolved in the water and the fish are suffocating, we really don't care about what the pH value is. The corrective action is to change the water or to strongly aerate the water in order to remove the CO2. When this happens, the pH rises rapidly and this is never a problem. It's the correct behavior and fauna will not suffer sudden pH change trauma. Their health will immediately improve. If any negative behavior is noted under this condition, then it is a strong indicator that some other agent is in the water or that some other malady is present.

It's a very similar story with TDS. Any solid or liquid that dissolves in the water will change the TDS. If that something is toxic, like organic waste then the TDS rise will have a negative impact. If the TDS rise is due to something innocuous, like fertilizer, then there will be no ill effects.

I think you'll find that different tanks experience different rates of TDS rise/fall based on the behavior of the hobbyist. I add a lot of fertilizer throughout the week so my TDS will rise sharply. When I change the water, it will fall. People who overfeed without changing a large amount of water will experience a TDS rise that can be considered unhealthy. Some people have hardscape that dissolves, so when they add CO2 the rate of dissolution from the gravel or rocks will increase the TDS. New clay substrate will typically adsorb many components from the water and some people will see a TDS fall. After some months, the surface of the clay gets filled with the adsorbed components and the TDS fall will cease. There are so many scenarios mate, it's difficult to cover all of them with a broad general statement. We always need therefore to understand the Why of pH or TDS change.

Hope this makes sense! :geek:

Cheers,
 
Each scenario has to be analyzed within the context of the original conditions and the agents responsible for the change of pH. To only look at the pH change itself without context is not meaningful and it is often what causes people more grief.
So let me spell it again then.

If PH would raise quickly from 5 to 15 what happens then?

If you would like to get the idea of this scenario please look more carefully in my last post, in context as you say.
I can see that you defend Sasha's comments vigorously because he is actually quoting your own writings.
It is to be expected from young lads that lack self identification and are looking for some recognition on forums. I don't mean to be rude. It is just a sad reality that I see on all forums. Folks picking up a smart fights to win public vote.

If you really want to comment everything in context you should do so every time.
I did not see you answering my comments in their full context, but only pulling parts that appear wrong according to your beliefs and banging the academic bible after that.

Please forgive me if I don't line up my words as you. After all I am not a scientist and do not speak or even understand your language as I am sure many others wouldn't either.

I am trying to explain things in simple terms as a hobbyist.

Alternatively I could stop posting as I did for a long time until recently just not to be on the way of the "hard science".

Please check in detail post #26 and Sasha's comment to that to get the picture in what "scientific" discussion you got involved in.

I am sure John who opened this tread got probably completely lost by now, because he never asked for smart deep answers, but for a practical advise.
 
Aquadream, I'm not even going to bother responding to that. I look forward to reading Clive's message when it eventually appears.

If the science is too complex, then let this be the message you take away from this thread:

Imagine if I put a plastic bag over your head and forced you to re-breathe the air you exhale.
 
If PH would raise quickly from 5 to 15 what happens then?
I spelled it out specifically for you in my previous response. I told you that it depends on the specific agent responsible for the pH rise. That is the context I mentioned. There are many types of acids that can drop the pH rapidly. Weak acids as well as strong ones can drop the pH quickly, but only the strong acids will cause problems. On the other side of the coin, there really are not many weak bases that can cause a dramatic pH rise that you propose. Only caustic bases can do that, and obviously these toxins would kill the fish for lots of other reasons long before any osmoregulatory issues would arise.

I'm OK with your exaggeration because I get that you are attempting to illustrate a point, however, when you play the "what if" game you cannot just make up any scenario that comes to mind. The scenario must fit reality. Perhaps that is the difference between a simple hobbyist and a scientist. The scientist understands, to some extent, the rules of reality. That's why, in my previous post, I provided you with some alternate scenarios which were much more real world and which could actually happen. As BigClown said,

Ph5-15 if that happened in my tank i'd think someone was adding caustic soda crystals.
And so what happens is the person adding caustic soda to the tank is committed to the Tescadero Institute for the Criminally Insane.

For a re-visit to a less psychotic scenario:
Imagine that a large fish died unnoticed, it's body trapped and hidden in the undergrowth and decaying. The CO2 turns off at night and the pH rises from it's daytime acidic low to perhaps, above 7.0. The NH4+/NH3 equilibrium comes into play in such a scenario. So lots of times, people ask about fluctuating pH and whether it's dangerous, and the answer is, that the pH itself has no effect, however, the behavior of ammonium/ammonia will have an effect that has nothing to do with osmoregulation.

I also think that it's a bit unfair to Sacha as well as to the OP, as well as to others reading the thread. Fair enough if you don't understand the depth of the explanations, but I'm sure others have grasped at least the basics. You specifically asked the "what if?" and so, it was answered, hopefully, to the satisfaction of some. If you required additional clarification, then please advise.

Cheers,
 
I have been in deep thought recently with regards to hypothetical scenarios within the planted aquarium conumdrum. To tell the truth i cleared my mind by referring to calculus.

It is as clive and sacha have said, there are just to many variables. To even differentiate the variables to give a yes/no answer on a function like what specific level or limit of co2 addition will kill fish is simply un achievable and wholly unrealistic. This "simple" statement requires deep and lengthy differentiation to reduce the variables to a point where we can define limit and max and thats on 1 aquarium as we all know there is no "ideal" situation, Otherwise we'd all have tanks like amano and plantbrain.

What am i trying to say in support of the argument? Well, know the dependant factor that will cause all of the variables associated with it. Analysis leads to complex arguments, often ending in a heated debate. But the cause of ill fish health and plant failure is almost always dependant on one fact, something that we did to aquarium X caused something variables of varying magnitudes to the Nth term.

I wish there could be a magic formula to calculate a hypothetical situation, alas it is not to be.

Relax, sit back, keep a journal, make small and infrequent adjustments and all will be fine, know your dependants, light, dosing and by means of record keeping monitor the changes. Try not to use psuedoscience to explain complex scenarios. And above all else, just enjoy yourself.

Rich
 
Hi all,
The fish don't care about the pH changing. They care about whatever happened to cause the pH to change. If the pH change was caused by a significant change in the exchange mechanism, then it changes the chemical capability of the water. The water will behave in a different way in relation to other chemicals. If the pH change was caused by dissolution of a very weak acid, the chemical composition of the water remains basically the same. The dissolved acid is too weak to change the way in which the water behaves in relation to other chemicals. All the chemical processes/ reactions that happen will be virtually unaffected by the extra acid, and will remain pretty much the same.
Just to say straight away that I'm not a CO2 user, as I can find quite enough ways to kill my fish without asphyxiating them, but Clive and Sacha are right in saying that changes in pH caused by changing the CO2 ~ HCO3 equilibrium don't effect the fish.
If you have a look at this thread there is some more explanation <http://www.ukaps.org/forum/threads/co2-in-the-planted-aquarium.2270/page-2#post-295689>.

I think another problem is that people who have experience of pH in strongly buffered systems (like you might use for Rift Lake Cichlids) then extrapolate their (entirely valid) experiences to soft, low conductivity water. The problem is that in heavily buffered water falls in pH are caused by large changes in water chemistry, but as water approaches pure H2O pH becomes a less and less meaningful measurement.

Rather than thinking of pH as an absolute measurement, I find it easier to think of it as a ratio, and rather than thinking of rather abstract H+ and O-H ions, I think of pH as "grains of sugar" in a 2 pan balance, with one pan "acids" and the other "bases".

If the amount of sugar in both pans is balanced, the pH is pH7. You can have a grain of sugar in either pan, a sugar cube in either pan or a 2 kg bag in either pan and the pH is still pH7, as long as we are in balance.

If you add a grain of sugar to the "acid" pan that already contains a grain of sugar, you now have twice the mass of "acids" compared to "bases" and the pH falls to a fairly low level, but we've only added one grain of sugar. If we then repeat the exercise with the balanced 2 kg bags, the added grain of sugar to the acids side now makes no practical difference to the balance and the pH remains at pH7.

If you now think of the "acid" grain of sugar as a "H+ ion donor" and the "basic" grain of sugar as a "H+ ion acceptor", we are pretty close to understanding pH.

I hope that helps

cheers Darrel
 
I am sure John who opened this tread got probably completely lost by now, because he never asked for smart deep answers, but for a practical advise.
Yes, this thread has deviated somewhat from my original question. But it's all good stuff even if it gets a bit heated at times.

I have decided to go with 10 - 15ppm. Today, I made up my 2°dH KH 'reference' for my JBL CO2 drop checker. I don't know how accurate it is as I used the NT Labs test kit but it would appear that KH is difficult to measure reliably. Apparently, Hanna Instruments and La Motte make good KH test kits. The Hanna Instruments kit costs £36. Which test kits do you guys use to accurately measure KH?
 
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Salifert do a great KH kit. It's a titration test which means it's very accurate.
 
All my test kits are from Macherey-Nagel. Company that produces all sorts of tests for laboratories of any kind including those that control the municipality water supply.
 
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