Hey, sounds like a pretty complex problem. The calculated pH will depend on what acid you use to buffer the solution... you can use any weak acid with its base salt to make a buffer. Sulfuric is a strong acid, so you'd probably have to use sulfate and bisulfate salts instead of the actual acid.
If I remember right, GH doesn't have much of an effect on buffered pH, but KH does. If you're lowering carbonate to 10 ppm then it should make a big difference in a buffered solution.
The pH of buffer depends on the pKa of the acid you use, and unfortunately, the most common is phosphate for a pH of 7. The equation is pretty simple (Henderson-Hasselbach equation):
The "Ka" is the dissociation constant for the acid (have to look this up). The "pKa" is the negative log of the Ka. Then you add the log of the ratio of the base to the acid. The ratio determines the pH, the actual *amount* of base (A-) and acid (HA) you use determines how strong the buffering is.
Soo... for a pH of 7, with phosphate being out... there are a lot of organic buffers out there, but I don't know if they'll be suitable. If you can get ammonium acetate, that can work as a buffer just by itself according to this site:
Ammonium acetate is pretty cheap if you can find a supplier. In practice, the easiest way to ensure your pH is to use a meter (or pH paper), since there are so many variables.
Good luck! Heh, I'm actually pretty rusty with this stuff ;)
Two problems with ammonia sollutions. Ammonia + fish = dead fish. And there are bacteria in there that feed on ammonia, so the buffer would be consumed by that bacteria in short order. The fish themselves produce ammonia, but bacteria break it down into nitrite. There is then another group of bacteria that feed on the nitrite and reduce it to nitrate. All three chemicals of course reduce ph, and ammonia and nitrite are in quantities less than .25ppm thanks to the bacteria. However Nitrate stays around, and exists usually between 5ppm and 15ppm in a healthy well maintained aquarium, but can get as high as 50ppm before the fish die and algae take over.
In my case I also have plants, that absorb some of all three of those. There are also bacteria that will feed in nitrate but they require anaerobic conditions, and release hydrogen sulfide. The also absorb micro nutriants, some of which for them is Mg and Ca, which of course lowers hardness, which lowers my buffering capacity.
I've got some commercially available buffer. They just never say what all is in them and that bothers me. The only thing that gives me any clue is the MSDS. Even then they are as vague as possible. I guess to protect trade secrets. Sure makes the msds useless.
so we know it's bisulfates, which ones we don't know.
ACGIH TLV Other Limits NA 5 mg/m 3 time weighted avg.
and I suppose that gives us some idea of concentration, but I don't think mole strength can be calculated from that.
They do claim that it "it converts carbonate alkalinity (KH) into available CO2." That means a temporary drop in ph, but only till the co2 is used by my plants, or escapes.
They give just as useless information for the Alkali buffer. Alkali buffer:
Components (Chemical Identity; Common Names (s)) Proprietary powdered non- phosphate buffer salt
This would all be much easier if they would just tell me what is in the shit. They don't because 1.we would see they are full of shit for the most part. 2. most people don't really go about the problem with any level of scientific method. They just put in a bit and hope for the best.
In any case, they say to use both buffers in specific ratios with reverse osmosis water to restore it to natural levels.
I've done this with the tap water, and it works at least. kh went from about 1 degree to 4 degrees, ended up around a ph of 7.0 I think i'll just give up trying to be scientific about the thing, and just do it by guess work like everyone else does. God I hate that though.
If I remember right, GH doesn't have much of an effect on buffered pH, but KH does. If you're lowering carbonate to 10 ppm then it should make a big difference in a buffered solution.
The pH of buffer depends on the pKa of the acid you use, and unfortunately, the most common is phosphate for a pH of 7. The equation is pretty simple (Henderson-Hasselbach equation):
http://en.wikipedia.org/wiki/Henderson%E2%80%93Hasselbalch_equation
pH = pKa + log([A-]/[HA])
or,
pH = -log(Ka) + log([A-]/[HA])
The "Ka" is the dissociation constant for the acid (have to look this up). The "pKa" is the negative log of the Ka. Then you add the log of the ratio of the base to the acid. The ratio determines the pH, the actual *amount* of base (A-) and acid (HA) you use determines how strong the buffering is.
examples:
http://chemistry.about.com/od/acidsbase1/a/hendersonhasselbalch.htm
http://www.chembuddy.com/?left=pH-calculation&right=pH-buffers-henderson-hasselbalch
Soo... for a pH of 7, with phosphate being out... there are a lot of organic buffers out there, but I don't know if they'll be suitable. If you can get ammonium acetate, that can work as a buffer just by itself according to this site:
http://lclane.net/text/acetate.html
Ammonium acetate is pretty cheap if you can find a supplier. In practice, the easiest way to ensure your pH is to use a meter (or pH paper), since there are so many variables.
Good luck! Heh, I'm actually pretty rusty with this stuff ;)
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"If you're lowering carbonate to 10 ppm then it should NOT make a big difference in a buffered solution."
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In my case I also have plants, that absorb some of all three of those. There are also bacteria that will feed in nitrate but they require anaerobic conditions, and release hydrogen sulfide. The also absorb micro nutriants, some of which for them is Mg and Ca, which of course lowers hardness, which lowers my buffering capacity.
I've got some commercially available buffer. They just never say what all is in them and that bothers me. The only thing that gives me any clue is the MSDS. Even then they are as vague as possible. I guess to protect trade secrets. Sure makes the msds useless.
acid buffer: Components (Chemical
Identity; Common Names
(s))
Proprietary powdered
bisulfate salts
so we know it's bisulfates, which ones we don't know.
ACGIH TLV Other Limits
NA 5 mg/m 3 time weighted
avg.
and I suppose that gives us some idea of concentration, but I don't think mole strength can be calculated from that.
They do claim that it "it converts carbonate alkalinity (KH) into available CO2." That means a temporary drop in ph, but only till the co2 is used by my plants, or escapes.
They give just as useless information for the Alkali buffer.
Alkali buffer:
Components (Chemical
Identity; Common Names
(s))
Proprietary powdered non-
phosphate buffer salt
This would all be much easier if they would just tell me what is in the shit. They don't because 1.we would see they are full of shit for the most part. 2. most people don't really go about the problem with any level of scientific method. They just put in a bit and hope for the best.
In any case, they say to use both buffers in specific ratios with reverse osmosis water to restore it to natural levels.
Acid Buffer Alkaline Buffer pH
1 : 0.5 5.0
1 : 1.0 6.0
1 : 1.3 6.5
1 : 2.0 7.0
1 : 2.5 7.5
1 : 4.0 8.0
I've done this with the tap water, and it works at least. kh went from about 1 degree to 4 degrees, ended up around a ph of 7.0 I think i'll just give up trying to be scientific about the thing, and just do it by guess work like everyone else does. God I hate that though.
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