Gh 8 kh 1 250tds
Yes technically water can be soft and have a high tds. But it probably isn’t particularly common for tap water.
When people say water is “soft” usually what they mean is that it’s low in Kh (carbonates) and or GH (calcium and magnesium). That is all those two tests measure for, those three components.
TDS = total dissolved solids. So this measurement is telling you the total of everything dissolved in the water, including the calcium, magnesium, carbonates, and a myriad of many other things that can be dissolved in water.
Let’s say you take a bottle of distilled water with tds of 0 and add a box of table salt. Will the tds go up? Yes, the more salt you add the higher it will go as long as it keeps dissolving. Anything dissolved in the water raises tds. Will the GH or Kh go up? No, because sodium chloride as we can deduce by the name has no effect on carbonates, calcium or magnesium, it contains none of those components so it cannot increase Kh or GH.
But in real life we have to look at what usually happens in regards to our water supply. If our tap water is coming from a deep underground reservoir which lies below certain types of rocks, as that water percolates down through the ground it can pick up things from the rock, for instance calcium, magnesium or carbonates. And often the rock that it gets these things from are high in other minerals too, for instance iron. So usually when someone has “hard” water, they are high in a lot of things, kh, GH, and other things too, all combining to create a high tds.
As a side note many people with very hard water use water “softeners” which lower the hardness but don’t lower tds because they way they work is by exchanging the minerals with something else like sodium. So the water becomes “soft,” but still has the same tds with the sodium increased proportionally to the other things being removed.
On the other hand, if our tap water is coming from a source above ground like a surface reservoir, or in my case a relatively shallow well in ground that has low amounts of dissolvable minerals in it, when the rain falls (which starts off essentially at 0 tds) it doesn’t have to percolate through a lot of rock first where it would pick up “hardness” before it’s pumped into the house. Therefore both the Kh and GH are low.
So in real life the characteristics of water depend mainly on the geology of the area and location the water is coming from before it gets pumped into your house, but we can see why someone who has “soft” water is likely to have a low tds also.
I don’t think tds per se has any particular effect on plants. I would say the problem is that for many the high tds is coming from sodium in the water. which is bad for plants.
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