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Old 03-16-2010, 05:44 AM   #1 (permalink)
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Default Understanding GH & TDS & Hardness

My TDS meter says I have 280ppm. TDS measures conductivity and pretty much everything that is in the water that is not pure H2O. GH measure only Calcium and Magnesium. When people say they have soft or hard water, they usually mean GH. So, what if my TDS reading is like over 1000ppm and no ca or mg, is that still consider super soft water? How will high TDS reading affect plant? I'm sure adversly, it could be high in sodium, organic waste, chloride, potassium, etc... In this hobby, It seems that we place too much emhasis on GH and not enough on TDS. I think more people should start measuring their TDS to get the complete picture.

So my 280ppm TDS reading consist of:
40ppm Ca
10ppm mg
35ppm K
15ppm N
5ppm P
<50ppm of sulfar


So is that consider soft, medium, or hard water? I think my GH is around 4-5 right? 17ppm of ca = roughly one degree of GH and 7ppm of mg = roughly one degree of GH?
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Old 03-16-2010, 07:51 AM   #2 (permalink)
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Default Re: Understanding GH & TDS & Hardness

The individual electrolytes donít add up to 280 ppm. I wonder if the test already accounted for other electrolytes such as dissolved metals, and non-electrolytes, such as suspended particles? What kind of TDS meter are you using?

A TDS of 280 ppm would be considered hard water. If we only look at Ca & Mg for hardness, you have 50 ppm (40 ppm Ca + 10 ppm Mg Ė by arithmetic of fractions with a common denominator) , which is less than 4 German degree, and that would be very soft water. It can be misleading if a test kit would test hardness by looking at only Ca & Mg when there is a fair share of other electrolytes and particles in the water. If Ca & Mg are the major electrolytes as compared to the rest of other electrolytes, the test may have validity within some range. I agree with you that serious aquarists would consider TDS a better indication for water hardness, especially in the case of your water TDS electrolyte breakdown.

That is an interesting case youíve brought up. Iíd like to see other comments on this issue.

As for high TDS affecting plants, a heavy fertilizer runoff into rivers and ponds can kill aquatic plants and fish near the vicinity, and cause algae bloom.

http://www.waterfiltersonline.com/tds-sources.asp
http://theaquariumwiki.com/TDS
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Old 03-18-2010, 10:37 PM   #3 (permalink)
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Default Re: Understanding GH & TDS & Hardness

It is not so simple as just adding things up. The GH test for example compares the things it is testing to calcium carbonate.
http://en.wikipedia.org/wiki/DGH
Similarly the Ca and Mg tests may not report Ca and Mg, but some other equivilant. (Sorry for being so vague, it has been a while since I have looked into these details)
http://www.thekrib.com/Plants/CO2/ha...arryfrank.html

My tap water is just under 300 ppm per my TDS meter, and my soft water fish that were hatchery raised are OK, including Discus, but I need RO for German Blue Rams.
GH and KH are around 4-5 German degrees of hardness, and these do not add up to 300 ppm, either, but under 200 ppm, even on a day when both are reading 5 degrees.
My hard water tanks (Lake Tanganyika) has a TDS closer to 800 ppm. My Brackish water tank (SG 1.004) has a TDS of about 2000 ppm.

I would call your water fairly soft, fine for hatchery raised soft water fish, but look into RO for the most delicate fish, and for breeding soft water species.

Last edited by Diana K; 03-18-2010 at 10:52 PM..
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Old 03-19-2010, 06:31 AM   #4 (permalink)
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Default Re: Understanding GH & TDS & Hardness

Thanks Diana, that's what I thought too, that my water is consider fairly soft. I remember Tom saying that his TDS was around 300ppm as well and he consider his water to be soft and rich with nutes.

In the past, I kept my water at around 100ppm and my plant did not respond as well. Increasing the TDS to the currrent level seems to make my plant more rich in color and more vibrant.
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Old 03-19-2010, 02:14 PM   #5 (permalink)
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Default Re: Understanding GH & TDS & Hardness

There is a good thread discussing this subject over at Tom's site right now.
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Old 03-19-2010, 04:53 PM   #6 (permalink)
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Default Re: Understanding GH & TDS & Hardness

There are not many plants that will thrive when the water is so low in minerals as to measure just 100 ppm TDS. Most plants that we keep in aquariums come from somewhat harder water than that, or, even if they come from soft water, they can thrive in harder water just fine.
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Old 03-19-2010, 06:49 PM   #7 (permalink)
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Default Re: Understanding GH & TDS & Hardness

Quote:
Originally Posted by Diana K View Post
It is not so simple as just adding things up. The GH test for example compares the things it is testing to calcium carbonate.
http://en.wikipedia.org/wiki/DGH
Similarly the Ca and Mg tests may not report Ca and Mg, but some other equivilant. (Sorry for being so vague, it has been a while since I have looked into these details)
http://www.thekrib.com/Plants/CO2/ha...arryfrank.html
Diana,

Even in approximation, they do add up in simple arithmetic fashion either in TDS or the general GH because ppm unit is the same as mg/L or g/1000000 mL (part per million). The cations Ca++ & Mg++ each has a specific weight of their own. Of course test kits canít measure the weight of each cation, so they sense and approximate the total number of the cations in a finite volume of water, then interpret the result in total weight per water volume expressed in ppm or in degree. By the same token, the test kits can also use the anions numbers (bicarbonate, carbonate, sulfate), as each of them corresponds to a cation Ca++ or Mg++ into a weight value to come to the same ppm result.

Quote:
Originally Posted by Diana K View Post
There are not many plants that will thrive when the water is so low in minerals as to measure just 100 ppm TDS. Most plants that we keep in aquariums come from somewhat harder water than that, or, even if they come from soft water, they can thrive in harder water just fine.
Itís clear to me now that there is no correlation of hardnesses between TDS and GH. GH mainly refers to the measurement of Ca & Mg only, while TDS includes many more things in the water. I didnít pay much attention to TDS before, but this thread certainly gives me an incentive to own a TDS meter to know which electrolyte is exceedingly in excess or lacking to the detriment of plants or fish health. Thanks.
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Old 03-17-2011, 03:38 PM   #8 (permalink)
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Default Re: Understanding GH & TDS & Hardness

Captain of the two year old threads at it again. I just like helping those that stumble on this info.

Quote:
Originally Posted by goldier View Post
It’s clear to me now that there is no correlation of hardnesses between TDS and GH. GH mainly refers to the measurement of Ca & Mg only, while TDS includes many more things in the water.

GH is total hardness and that is more than just Ca and Mg ions, but it generally speaks of Ca and Mg because all others are usually too low to consider measurable.

TDS is correlated to gh and frankly everything else in water that can be a solid. TDS is what you get if you let all the water evaporate out of a container. Total unDissolved Solids

Quote:
I didn’t pay much attention to TDS before, but this thread certainly gives me an incentive to own a TDS meter to know which electrolyte is exceedingly in excess or lacking to the detriment of plants or fish health. Thanks.
Well TDS is a pretty broad term and especially how it is measured electronically it can be close but not accurate. It especially will not tell you anything about which ions are in a solution or what is lacking. It is better to think of it as a guideline to follow. Similar to pH. You don't have to hit it exact, but make it stable. TDS is the overall thing to look at for will my fish/shrimp be comfy. obviously there is more to it than tds.

Last edited by cliffclof; 03-17-2011 at 03:43 PM..
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