# Magnesium Sulphate in Hard Water?



## Aqua sobriquet (25 Jun 2012)

On the TNC site it says that you may not need Magnesium Sulphate if you are in a hard water area.
Do those of you with hard water add it or not?   

http://www.thenutrientcompany.com/aquarium/calculators/


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## Matt Warner (25 Jun 2012)

Hi, I have moderately hard water, but I add magnesium just to make sure I have enough. If I leave out the magnesium, I find that my plants suffer from deficiency. Also, my water quality report doesn't say how much magnesium is in my tap water. Just because your water is hard, doesn't mean it is hard because of magnesium, it could be calcium instead which is making it hard. Magnesium sulphate is so cheap, its not really an issue to add it, as it is the cheapest of the dry salts. The only way to know if you need it is to not add it to your macro mix and see what happens. If you notice your plants start showing deficiency, then add it again.


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## spyder (25 Jun 2012)

When I researched EI and started mixing I was supposed to be using 6 tsp's. I cut it down to 4 tsp's and things seem ok. Water is fairly hard around here I believe, I haven't tested any water, tank or tap.

I might try and whittle it down a little more to see what happens.

If you don't need then it's pointless adding it but adding it does add that level of protection against a possible deficiency which is what EI is intended to do.


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## dw1305 (26 Jun 2012)

Hi all,


> On the TNC site it says that you may not need Magnesium Sulphate if you are in a hard water area.


 This has come up before <http://www.ukaps.org/forum/viewtopic.php?f=35&t=14225> and it definitely isn't true if you live in most of the UK. You can get areas where the limestone has become dolomitic or magnesian limestone (calcium magnesium carbonate CaMg(CO3)2), and there are small deposits of dolomite in the Carboniferous age limestones of N. Scotland, Mendips and Llangollen area (via "supergene enrichment"), but the vast majority of tap water will contain very little magnesium (and none at all if the water is from a chalk aquifer). 

*Geological bit*
There area couple of richer sources of magnesium, a thin band of Permian age magnesian limestone running along the E edge of the Pennines, from Nottingham northwards 





> _The succeeding Permian (290-248 million years ago) Period is represented in Nottinghamshire by the Magnesian Limestone, which is so named because the rock contains the magnesium rich mineral ‘dolomite’. This limestone was deposited in a relatively shallow landlocked sea extending from northeast England to Poland ......... Due to the landlocked nature of the sea and high temperatures, deposits of gypsum and anhydrite (collectively known as evaporites) derived from evaporation of the seawater, are found throughout the rock sequence_


 Other sources are the Lizard peninsula serpentine rocks 





> _Serpentine and gabbro produce magnesium ... rich soils and it is the resulting alkalinity of the soils that has enabled a large number of quite rare plants to thrive on these parts of The Lizard._


 and there are a few other evaporite deposits, like the one at Epsom (hence "Epsom Salts"), but otherwise the limestone rocks (that forms the hard water aquifers) are almost entirely devoid of magnesium. 

There is a map towards the end of the BGS report  "Commodity profile MAGNESIUM - British Geological Survey"<http://www.bgs.ac.uk/downloads/start.cfm?id=1402>.

cheers Darrel


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## GHNelson (26 Jun 2012)

Good response Darrel  
hoggie


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## Matt Warner (26 Jun 2012)

Thats a very interesting read Darrel, I was sure I had read about that before somewhere but couldn't remember where. So basically then, the majority of Britains hard tap water area is buffered from Calcium rather than Magnesium.


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## Aqua sobriquet (26 Jun 2012)

Thanks very much Darrel, you've come up trumps again   

Perhaps someone should tell TNC!


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## dw1305 (27 Jun 2012)

Hi all,


> So basically then, the majority of Britains hard tap water area is buffered from Calcium rather than Magnesium.


 Yes. This would be the same for the majority of the World's carbonate rocks. There are big deposits of magnesium in evaporites (from sea water) in some parts of the world, and exposures of magnesium rich mafic rocks like our Lizard serpentine rocks in others, but not in the UK. 

I think the original TNC advise possibly applies to parts of the mid-west, California and SE of the USA ("Floridan aquifer"), where the artesian water is relatively magnesium rich. Tom may well be able to add some more detail.

cheers Darrel


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