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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.

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

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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