TDS question
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From a good article (although a little reefy):
http://www.advancedaquarist.com/2002/2/chemistry
Alkalinity is defined in different ways for different applications. In the chemistry of natural waters, there are several types of alkalinity that are encountered. Each of these is a measure of how much acid (H+) is required to lower the pH to a specific level.
I'll come back to some of the other types of alkalinity later, but for now we will confine our discussion to the "total alkalinity." frequently referred to as TA.
TA is defined as the amount of acid required to lower the pH of the sample to the point where all of the bicarbonate [HCO3-] and carbonate [CO3--] could be converted to carbonic acid [H2CO3].
<snip>
I say "could be converted" because regardless of the pH, there will always be some bicarbonate and carbonate present, but at some pH there are enough protons (H+) in solution that if they were combined with the bicarbonate and carbonate present, it would all be converted to carbonic acid.
The precise endpoint of a total alkalinity titration isn't always the same pH, but rather depends a bit on the nature of the sample (both its ionic strength and its alkalinity). For normal seawater, this endpoint is about pH = 4.2. In freshwater it depends strongly on the alkalinity, with an endpoint of pH = 4.5 for an alkalinity of 2.2 meq/L, and pH = 5.2 for an alkalinity of 0.1 meq/L.
Consequently, total alkalinity tests have been invented that determine how much acid is required to lower the pH into the 4-5 range. Later in this article I'll describe how these tests kits are measuring alkalinity.
<snip>
Finally there is the German term dKH (degrees of carbonate hardness), or just KH (carbonate hardness). Strictly speaking, it is the same as the carbonate alkalinity (AC in equation 8). Unfortunately, it is a very confusing term, as it has nothing to do with hardness. Further, it has been corrupted by the marine aquarium hobby to mean the same as total alkalinity, and every test kit that tests for dKH with a single titration is giving total alkalinity. The only kit that I am aware of that even makes a distinction between carbonate alkalinity and total alkalinity is one of the Seachem kits (Reef Status: Magnesium, Carbonate, & Borate) and it thankfully doesn't use the term dKH at all. Consequently, most hobbyists should think of dKH as simply another measure of total alkalinity. The results obtained with such a kit (dKH) can be divided by 2.8 to yield the alkalinity in meq/L.
Matt
http://www.advancedaquarist.com/2002/2/chemistry
Alkalinity is defined in different ways for different applications. In the chemistry of natural waters, there are several types of alkalinity that are encountered. Each of these is a measure of how much acid (H+) is required to lower the pH to a specific level.
I'll come back to some of the other types of alkalinity later, but for now we will confine our discussion to the "total alkalinity." frequently referred to as TA.
TA is defined as the amount of acid required to lower the pH of the sample to the point where all of the bicarbonate [HCO3-] and carbonate [CO3--] could be converted to carbonic acid [H2CO3].
<snip>
I say "could be converted" because regardless of the pH, there will always be some bicarbonate and carbonate present, but at some pH there are enough protons (H+) in solution that if they were combined with the bicarbonate and carbonate present, it would all be converted to carbonic acid.
The precise endpoint of a total alkalinity titration isn't always the same pH, but rather depends a bit on the nature of the sample (both its ionic strength and its alkalinity). For normal seawater, this endpoint is about pH = 4.2. In freshwater it depends strongly on the alkalinity, with an endpoint of pH = 4.5 for an alkalinity of 2.2 meq/L, and pH = 5.2 for an alkalinity of 0.1 meq/L.
Consequently, total alkalinity tests have been invented that determine how much acid is required to lower the pH into the 4-5 range. Later in this article I'll describe how these tests kits are measuring alkalinity.
<snip>
Finally there is the German term dKH (degrees of carbonate hardness), or just KH (carbonate hardness). Strictly speaking, it is the same as the carbonate alkalinity (AC in equation 8). Unfortunately, it is a very confusing term, as it has nothing to do with hardness. Further, it has been corrupted by the marine aquarium hobby to mean the same as total alkalinity, and every test kit that tests for dKH with a single titration is giving total alkalinity. The only kit that I am aware of that even makes a distinction between carbonate alkalinity and total alkalinity is one of the Seachem kits (Reef Status: Magnesium, Carbonate, & Borate) and it thankfully doesn't use the term dKH at all. Consequently, most hobbyists should think of dKH as simply another measure of total alkalinity. The results obtained with such a kit (dKH) can be divided by 2.8 to yield the alkalinity in meq/L.
Matt
Also...
I think that TDS (or total dissolved solids) can be misleading because TDS is comprised of inorganic salts (principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates) as well as organic matter that is dissolved in water.
Rift lake water and salt water can have high TDS because they have lots of inorganic salts in them.
Water without lots of salt in it (i.e. blackwater) can have high TDS because of lots of dissolved organic stuff (i.e. nitrates and the like).
TDS gives you a total of the two...
Matt
I think that TDS (or total dissolved solids) can be misleading because TDS is comprised of inorganic salts (principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates) as well as organic matter that is dissolved in water.
Rift lake water and salt water can have high TDS because they have lots of inorganic salts in them.
Water without lots of salt in it (i.e. blackwater) can have high TDS because of lots of dissolved organic stuff (i.e. nitrates and the like).
TDS gives you a total of the two...
Matt
I'm guessing you measure conductivity? That will give you an approximation of total dissolved ions in solution but will not measure other neutral dissolved solids. As far as relating it to pH, kH or gH, you can't with certainty so just get a cheap GH and KH api kit.
Well I found this table for gH:
General Hardness Table
0 to 4 dH 0 to 70 ppm Very Soft 4 to 8 dH 70 to 140 ppm Soft
8 to 12 dH 140 to 210 ppm Medium Hard
12 to 18 dH 210 to 320 ppm Fairly Hard
so I was wondering if this would be accurate, since according to this table if the middle column is TDS ppm readings my dH would be somewhere around 14 maybe? I also know that the higher the dH value is, the pH will be higher and if dH is lower the pH will be lower. So there won't be any confusion I'm talking about tap water so it's freshwater. I know that the salts in saltwater or reef tanks will add to the TDS. I was wodering if I can get some approximate values on other water parameters based on the TDS.
It is not that straight forward. I'm no water chem expert but I will give it a shot, GH is a measure of Mg and Ca ions in the water and KH is the measure of the alkalinity of the water. Conductivity (I am assuming what you are calling TDS) is a measure of all dissolved ions in the water. You could have a really high conductivity but if all the ions were Na+ and Cl- you would have very soft water but at the same time high total dissolved solids. Why not get an $8 api hardness kit and see what your KH and GH are? Then you will have all the info, conductivity, GH, KH and PH without guessing
Can't find any API hardness kits, took me forever to find a TDS meter. Asked a guy that works with water filters to mesure it for me. They don't sell those kits in fish stores around here. Anyways I get the picture. So since my total dissolved solids is 250 ppm there could be organic and other kinds of ions in the water so my water could be softer. Also from what I understood technically it can't be harder then 14.
It's impossible to make a determination on your KH/GH from a TDS test. GH is a measure of the magnesium and calcium ions in your water. KH is your buffering capacity (not exactly what or how it's measuring). TDS is any and all particles, all of which have some effect on a fish's osmotic regulation.
Take for example water that's been passed through a household water softener. These work on the ion exchange principle. They pull out magnesium and calcium (your GH) and exchange them with sodium ions (salt). So, a GH test should read 0, or basically no hardness. But if you do a TDS test, it could by sky high because of the sodium ions.
That is why you need to test both TDS and GH to get a good understanding. The waters where discus come from have TDS of 10-30ppm and extremely low hardness/GH levels of 1-2dh
Take for example water that's been passed through a household water softener. These work on the ion exchange principle. They pull out magnesium and calcium (your GH) and exchange them with sodium ions (salt). So, a GH test should read 0, or basically no hardness. But if you do a TDS test, it could by sky high because of the sodium ions.
That is why you need to test both TDS and GH to get a good understanding. The waters where discus come from have TDS of 10-30ppm and extremely low hardness/GH levels of 1-2dh