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Originally Posted by banderbe  In other news, I removed the drop checker from my tank and stuck it on my mirror in my bathroom. Within a day the color went back to blue.
I had also taken a glass full of water from the aquarium and left it out over night to degass.
I submersed the drop checker (now blue) into the glass of water, and it is staying blue, confirming that indeed the CO2 level in the glass of water went way down.
So I guess I still have no idea why on Earth the drop checker's color stays green even after a night of surface aeration and no CO2.
Weird. But, I am comfortable in believing that green means good CO2 IF it is true that ONLY CO2 can enter the drop checker's water.
I still wonder why other acids in the tank water can't also enter a gas phase and enter the drop checker's water.
Hoppy, can you confirm for me the intent of the drop checker?
In a tank with a giant piece of drift wood, e.g. tons of tannic acid, your drop checker (not the membrane idea) should still give an accurate reading of CO2. Is that correct?
So there is the unstated assumption here that acids other than CO2 cannot pass through the gas pocket inside the drop checker.
I still want to know how we know that... |
We know it because there will be no distillation occurring unless the drop checker water and the tank water are at different temperatures. Acids are just water with ions in it, with more H+ ions than OH- ions. If the acidic water becomes a gas it has to be H2O molecules, not a mix of ions and molecules. Even if there were distillation, the distillate would be pure water with no ionic solutes. That's why distillation gives us water without any salts in it.
So, only gas can go across the air gap from one glob of water to the other. Oxygen, nitrogen, CO2 and any trace gases will also go across. Volatile organics such as alcohol will also go across the gap. But acids and bases won't, since by definition, they are ions, not molecules.
That is how I see it anyway. I'm a bit troubled by knowing I can smell muriatic acid, which certainly appears to mean the vapors I smell are gases and acid. Perhaps someone with a lot more chemical knowledge than I have would like to discuss this?