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BigDon
2017-Mar-01, 05:50 PM
Oddly enough, I've been wanting to ask this question since I first signed on here.

Too easily distracted.

Now originally I got this information from a translated 1930's German fishkeeping book.

The subject was keeping delicate aquatic animals alive in less than ideal conditions as an emergency measure.

Entire branches of the Amazon river, unlike most bodies of surface water, is very soft. It's both due to the geology, said branches tend to run over insoluble granites, and the biology as all those trees suck up every bit of calcium and carbonate they can get a hold of, thereby introducing it to the highly efficient organics recycling system and out of the water column.

So a lot of the fish and other organisms that come from the Amazon black water regions and similar bodies of water have a low tolerance for high carbonate levels in their tank water. Won't even go into the pH issues. This is also true of a lot of carnivorous plants though the threat that high carbonate content posses to them, it kills them, I don't know the details of.

Especially this effects reproductive success in fish. The common neon and cardinal tetras require the difference in osmotic pressures to inflate their eggs after ovulation. Kept in hard water the uninflated eggs form a plaque around the ovary, effectively sterilizing the fish. This is often not reversible.

So those are the issues.

Now this book claims that the carbonates in tap water can be rendered less harmful by boiling for three or so minutes. The author claimed that in a process similar to clay firing, boiling the water renders the carbonates a lot less soluble and therefore less harmful to the organisms in question. After cooling and aerating of course.

I've been wanting to ask Swift that question ever since I found out that he was not only a chemist, but a solvologist.

I also have a couple of aeration questions/observations for Dr Grant, but that's for later.

Swift
2017-Mar-01, 06:00 PM
I've been wanting to ask Swift that question ever since I found out that he was not only a chemist, but a solvologist.

What the heck is a solvologist?

Anyway.... boiling will decrease the amount of carbon dioxide in the water (as well as other soluble gases). I guess that would tend to drive the dissolved carbonate to (I would guess) hydroxides; I'm not up on the relative solubilities.

Found a good discussion about this from a retired chemist (http://www.chem1.com/CQ/hardwater.html)

Trebuchet
2017-Mar-01, 06:01 PM
I'm not expert, but I can't see how that could work. If anything, it would increase the carbonate concentration by boiling off water. Unless you're going to capture and condense the steam!

BigDon
2017-Mar-01, 06:29 PM
Treb, where do you live that three minutes of boiling on the stove drives off a gallon of water?

Trebuchet
2017-Mar-01, 06:53 PM
I didn't say that. But it's going to boil off some.

profloater
2017-Mar-01, 07:37 PM
There is temporary carbonate, calcium, and permanent, magnesium, the calcium deposits out by boiling, but surely a modern aquariumist would use reverse osmosis which removes all large molecules, then add back exactly what is required? Carbon dioxide dissolved in that water is as carbonic acid.

grant hutchison
2017-Mar-01, 08:08 PM
I presume the same phenomenon that leads to the deposition of limescale in kettles and boilers. There's an equilibrium in solution between calcium bicarbonate and calcium carbonate + carbon dioxide + water. When you boil the water, you drive off the dissolved carbon dioxide (as Swift says), which shifts the equilibrium to produce more calcium carbonate. When the water cools, the calcium carbonate precipitates out.
Given enough time, the cool water would reabsorb carbon dioxide and redissolve the calcium carbonate, but that's a bit of geological process. So you can throw away the calcium carbonate and use the cooled water for your fish.

I live in a soft water region, so never run into a problem with limescale. Except once, when the coffee room kettle at work started to grow the stuff at a completely mad rate. A bit of detective work revealed that one of my more logically impaired colleagues was afraid of tap water, and was bring bottles of mineral water from home, which she was boiling to make coffee for herself each morning. We explained the origins of the name "mineral water" to her in slow, careful syllables and persuaded her to bring in a flask from home in future (thereby scaling up her own kettle instead of ours).

Grant Hutchison

kzb
2017-Mar-02, 06:04 PM
I think it is connected to the solubility of calcium bicarbonate. Calcium bicarbonate is soluble, calcium carbonate virtually insoluble.

Like Grant says, boiling it will decompose bicarbonate and drive off the CO2 as gas. Excess calcium carbonate may then precipitate out.

Boiling it also removes most of the oxygen. Re-aerating it will re-introduce CO2 and bicarbonate. So I don't think it's a good idea.

If you were to add a few drops of acid to take the pH to about 4, boiled it and re-aerated it, that would keep out the bicarbonates. But I don't know what pH 4 water would do to your fish or their eggs.

BigDon
2017-Mar-02, 08:07 PM
I think it is connected to the solubility of calcium bicarbonate. Calcium bicarbonate is soluble, calcium carbonate virtually insoluble.

Like Grant says, boiling it will decompose bicarbonate and drive off the CO2 as gas. Excess calcium carbonate may then precipitate out.

Boiling it also removes most of the oxygen. Re-aerating it will re-introduce CO2 and bicarbonate. So I don't think it's a good idea.

If you were to add a few drops of acid to take the pH to about 4, boiled it and re-aerated it, that would keep out the bicarbonates. But I don't know what pH 4 water would do to your fish or their eggs.

Kzb, due to the lack of minerals and the presence of tannins, cardinal tetras have been recorded actively spawning in oxbows with pH's as low as 4.2.

Just filling and maintaining their tanks with de-ionized water drops the pH and at around 6.2 and lower the spawning becomes rather furious. I had a school of 50 of them at one time. One of the most beautiful tanks I ever had.

They got so healthy and robust I could feed them nightcrawlers! They would completely ball it and could consume a nine inch nightcrawler in 53 seconds as per a stopwatch.

BigDon
2017-Mar-02, 08:15 PM
Tetras spawn in low pH settings because;

One, that marks the rainy season.

Two, the low pH destroys bacteria and inhibits fungus. Hence the desire to lay eggs in it. Most microscopic pathogens of these creatures in the wild are protozoans and various animalcules.