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Magnesium supplement in a low-tech set-up

IvanF

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20 May 2015
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Am currently dosing my 310L Low-Tech set-up (no-CO2, muted lighting for 6 hour photoperiod, lots of floating plants, a small group of amano shrimp, no soil substrate) on a weekly basis with TNC Complete (NPK plus trace elements).

However, a month after set-up, I'm starting to see a few signs of a deficiency in my anubias - holes with a brown margin and browning tips/edges in mature leaves, small, crinkled new leaves. Nothing major as yet and no sign of algae - but it has got me thinking.

Having looked at my water report and the calculator below, I suspect that my hard tapwater contains plenty of calcium and no magnesium ions.
https://www.affinitywater.co.uk/docs/water-quality/TV064.pdf
http://www.lenntech.com/ro/water-hardness.htm

With this in mind, is it likely that my tank would benefit from additional Mg supplementation? TNC Complete contains:
1.5-0.5-6
1.5% N, 0.2% P, 5% K, 0.8% Mg, 0.08% Fe, 0.018% Mn, 0.002% Cu, 0.01% B, 0.01% Zn, 0.001% Mo, EDTA


Or am I approaching this from entirely the wrong angle?!

Cheers,

Ivan
 

ian_m

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Never rely on your water report as to supply plant fertilisation. Your water report will be at the water companies sampling point and a particular day which may not the same as your tap today.

Mg in UK tap water is generally not that high, thus if you think your plants need Mg, especially low tech, then add some Mg in form of Epsom salts (MgSO4.7H20) being cheap and easy.

Though generally mechanical damage to plants, holes, rips etc is due to over excited fish getting hungry or lack of carbon supply.
 
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Magnesium is a macro nutrient. It will affect old leaves. If the new growth is crinkled, I'd concentrate attention on trace elements. Since you are dosing TNC complete, just dose more of the lot.

holes with a brown margin and browning tips/edges

small, crinkled new leaves

Do you have pictures of the plants? Are other plants affected? What happened first, the old leaves damage or the new crinkled leaves?
For the holes with brown margins try more potassium which is a macro element. The crinkled new growth may not be even nutrient related but sort of a shock that will fix itself. However, if it is, it will be most likely trace elements related. I get that occasionally on my emergent plants and it seems micros sort this out.
Magnesium deficiency generally shows up as bleached leaves with green veins on older leaves. Necrosis doesn't really occur so none of the signs you describe suggests a magnesium issue.
 

IvanF

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Never rely on your water report as to supply plant fertilisation. Your water report will be at the water companies sampling point and a particular day which may not the same as your tap today.

Thanks Ian - fair point, and I was really only looking out of curiosity more than anything else (I had previously presumed that my hard tapwater would be full of both Ca and Mg ions).

At the same time, surely (total) hardness of tapwater is largely driven by the local geography/geology, and is therefore relatively constant when compared to other parameters?
 

IvanF

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Magnesium is a macro nutrient. It will affect old leaves. If the new growth is crinkled, I'd concentrate attention on trace elements. Since you are dosing TNC complete, just dose more of the lot

Thanks - seems like a sensible option. I've also got a bottle of TNC Lite knocking around (i.e. trace elements without NPK), so maybe I'll experiment over the next couple of weeks and see what delivers the best results......

The crinkled new growth may not be even nutrient related but sort of a shock that will fix itself.

That's interesting. I did wonder whether I should take any signs of deficiency with a pinch of salt for the first month or so, as the plants establish themselves in the new environment. Furthermore, all the floating plants (ceratopteris, salvinia, pistia and limnobium) all seem to be doing well since they were introduced a week or so ago......
 

ian_m

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I had previously presumed that my hard tapwater would be full of both Ca and Mg ions).
Not in UK. calcium only from chalk and limestone. Usually Mg comes from dolomitic limestone which doesn't occur in UK.
 

dw1305

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Hi all,
Magnesium deficiency generally shows up as bleached leaves with green veins on older leaves.
That is the one - "interveinal chlorosis" in the older leaves, because magnesium is mobile within the plant.

Plants don't need a huge amount of magnesium, but high levels of calcium can interfere with its uptake.
Not in UK. calcium only from chalk and limestone. Usually Mg comes from dolomitic limestone which doesn't occur in UK.
Pretty much, we do have a narrow band of magnesian limestone that runs from <"Nottingham north-east towards Durham">, but most of the aquifers in the S of the UK are chalk, which formed in a deep ocean basin and is 100% calcium carbonate.

Things are different in the States, where a lot of the USA limestone aquifers have experienced dolomotization (where magnesium ions have replaced some calcium ions), this is because the limestones formed in an "epicratonic sea" which repeatedly advanced and retreated ("Epsom Salts" is an evaporite mineral).

cheers Darrel
 
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