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Magnesium deficiency?

Kezzab

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18 Jan 2016
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1,396
Location
Carlisle
For the first time I've noticed what appears to be a nutrient deficiency, in both my current high tech tanks.

The big tank (90 45 45 plus sump = 200ltr ish) gets 75ml of TNC a week, the small tank (15ltr) has been getting a 50% wc every 48 hrs with a 2ml dose of TNC after each change.

It's the anubias in the small and the crypt in the large. Other plants seem ok, gowing well.Although in the big tank my bucephelandra mini red seems to struggle a bit.

My water is v soft, about 35TDs out the tap.

Assuming its magnesium, I have some TNC GH Boost in the cupboard, but not sure how much to add exactly.

Thoughts?
 

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X3NiTH

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13 Apr 2014
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Probably enough to raise the TDS about 10ppm from the initial 35 out the tap, there will be magnesium in the water but likely, 10:1 - 20:1 ratio of Ca:Mg.

Alternatively target an amount from the instructions that will give you a 1dGH rise via Mg addition in overall hardness in the water volume you are treating.

:)
 

X3NiTH

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Plant tissues contain a 3:1 ratio of Ca:Mg and the closer you are to this ratio the easier it will be for the plant to uptake Mg. A lot of flowing water body parameters I looked at showed a ratio roughly around 10:1 Ca:Mg, also this same ratio exist in the interstitial soils of ‘Forrest over Limestone habitat’ (Buce Habitat, my main focus) this correlates closely to the solubility of Mg which is 10x to that of Ca (Mg is quickly washed away), of course this all depends on the underlying Geology of the water source.

:)
 

ceg4048

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Plant tissues contain a 3:1 ratio of Ca:Mg and the closer you are to this ratio the easier it will be for the plant to uptake Mg.
This is not really true. All one has to do is supply non-limiting levels of nutrients and the plant will uptake what it needs. There is no correlation between the nutrient concentration in the plant tissue versus the concentration that must be supplied. This is yet another version of the Redfield Ratio theorem which is misleading. Plants accumulate and store nutrition in the tissues for future use. The amount that is stored depends on many factors such as availability, uptake efficiency as well as efficiency of the storage mechanism itself, the rate at which the nutrient is used and so forth.

One need never worry about in what ratio nutrients are fed as long as the concentration value is sufficient.
Just checked the water report, 9:1 Ca:Mg. What's the significance of the ratio in this context? I should know given I've probably read it a hundred times but I instinctively veer away from even basic chemistry.
All this means is that in typical water supplies Calcium is more prevalent than Magnesium simply because Calcium is ubiquitous, found in limestone, for example. Magnesium is much rarer.
It's exactly because of your instinct why it would be better to adopt a policy of ignoring ratios and to simply add as much of what is missing as you like. The plants will not care.

Cheers,
 

X3NiTH

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13 Apr 2014
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1,165
This is not really true.

Yeah I shouldn’t really have worded it quite like that. Ratioing everything can also be unhelpful because it gives the impression that there are specific limits while in reality as you say the plants will uptake what they need. I am well aware that plant content and environment content can be wildly different and this is not always expressed in plant tissue.

All good!

:)
 

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