De carbonaathardheid (waarvoor we dKH als eenheid gebruiken) stabiliseert de pH op ~pH 8 via het CO2/carbonaat-evenwicht (uitgaande van) 400ppm atmosferische CO2. De totale hoeveelheid anorganische koolstof (TIC/DIC) blijft hetzelfde, de vorm verandert alleen afhankelijk van de pH. Wanneer je CO2 toevoegt, verlaag je de pH, omdat je H2CO3 hebt toegevoegd, en dat is een protondonor (het “reserve” H+ ion).
The solubility of gases in water has only to do with pressure, temperature, and salinity. Salinity is the measure of Sodium (Na+) content only.
I’m not a CO2 user, but I think you are right, the level of dissolved CO2 depends upon Henry’s law, and if you assume 400 ppm CO2 in the atmosphere, standard pressure (1013mb) and a temperature of 20oC, then you have 1.35 x 10-5 mols l-1 of CO2 dissolved.
The RMM of CO2 is 12 + (16*2) = 44 (44g of CO2 in one Kg ), and if you work that out as ppm, it comes to ~0.6ppm (0.594ppm). The reason that that level is higher than the quoted 0.55ppm is just because the level of atmospheric CO2 has risen.
We have a CO2 monitor in the lab. and that usually sits at about 600ppm, but it is still along way from there to the dissolved 3 ppm quoted.
The only reference I could find for the 3ppm datum was the experimental work that George and Karla Booth did in the 1990’s <“CO2 loss in large aquariums“>.
Als u de pH/KH meet terwijl de tank in evenwicht is wanneer de CO2-injectie uit staat en voordat de lichten ’s morgens aangaan, zal het CO2-gehalte in de tank TYPISCH (maar niet altijd) overeenkomen met de evenwichtsniveaus met de atmosfeer, met inachtneming van de gaswetten – wat ongeveer 2-3 ppm zal zijn.
Duidelijker gezegd, terwijl CO2 in de atmosfeer een concentratie heeft van meer dan 400 ppm, stabiliseert de gemiddelde hoeveelheid in een open container met zuiver water rond de 2-3 ppm, wat “atmosferisch evenwicht” wordt genoemd. Een tank zonder CO2-injectie zal geen verhoogd CO2-gehalte hebben, TENZIJ er veel rottend organisch materiaal in het aquarium is OF TENZIJ er een behoorlijk aantal vissen zijn. Rottend organisch materiaal en vissen brengen beide koolstofdioxide in het water.
We have plenty of empirical evidence to demonstrate that cyclic pH changes or rapid pH changes due to CO2 injection is not harmful. I think people put the “cart before the horse” when it comes to pH. The danger posed by a pH change depends entirely on WHY the pH is changing. If the pH falls or rises rapidly due to the release of a toxic agent in the water column then the toxicity will be due to the effects of the toxic agent, not due to the pH. So for example if there is ammonia in the water and if the pH is low then this reduces the toxicity of the ammonia because of the higher ratio of the less toxic NH4+ to the more toxic NH3. If the pH were to suddenly increase dramatically then this would change the balance in favor of NH3 and so the condition of the water would be toxic – but this is due to an increase in NH3 and a reduction of NH4.
Conversely, if you were to add a strong acid to the tank this would result in a dramatic fall of the pH, but the toxicity will be due to the toxic acid, not just due to the pH. Strong acids disassociate to release massive quantities of H+ in the water column. These strong positive charges rips electrons from the orbital shells of tissue molecules and THAT’S why strong acids are dangerous, and that’s why they are used to generate electricity in batteries and so forth.
CO2 is a very weak acid and so, even though it releases H+ into the water, the quantity of H+ is very low. This causes the pH to drop dramatically but does not do harm to tissue structure. That’s why, for example, you can eat vinegar, which is a weak acetic acid, but you would think twice about putting battery acid on your salad, right?
The dangers of permanently high CO2 in the water depends entirely on how high the level is. The effect of hypercapnia (high CO2 content) is that the high partial pressure of the CO2 in the water column, restricts the flow of CO2 from the fish’s bloodstream into the water, so the CO2 concentration builds in the blood. This causes the blood to acidify and that becomes toxic. high bloodstream acidity reduces the ability of hemoglobin to hold Oxygen. The fish combat this by increasing the production of bicarbonate (HCO3-) to reduce the effects of the acid. However, there is a threshold whereby the bloodstream cannot produce enough HCO3- to buffer the blood. As the level of CO2 and blood acidity rises, the efficiency of the hemoglobin falls dramatically and the acidity also affects the function of nerve synapses, so the nervous system is endangered.
So it’s not a black-or-white choice between permanently high CO2 versus pH swings. One really has to understand the root causes as well as the concentration levels of the chemical agents affecting the pH or being affected by the pH. Either path has danger and so the danger must be assessed and managed.
De CO2-evenwichten in water