# Magnesium, do I need it/how to dose?



## Skizhx (Oct 12, 2010)

So I've been dosing with EI guidelines. I have a 29gal tank (estimated 20gal of actual water in it after substrate, driftwood, etc is factored in). 

The trace fertilizers I'm using don't have magnesium. Otherwise though, they're pretty well identical to CSM+B, little more iron in my ferts, that's the only difference.

Since doing EI (this is my 4th week) I've noticed that the new growth on my crypt. Wendtii (especially the var. 'gecko') is coming in quite yellow. I've also noticed what I suspect on my C. wendtii var 'gecko' to be the light leaves with darker veins that is attributed to magnesium deficiency.

Now here's where I'm uncertain. It seems that people feel with a GH above 6 that magnesium and calcium deficiency usually isn't a problem.

My tapwater is 9dGH and 3dKH. But again... My trace, unlike CSM+B has absolutely no magnesium in it.

So my first question... Does this sound like magnesium is the problem even with my water's hardness? Or would I be jumping to false conclusions. I sorta feel that with more iron than CSM+B a relatively slow growing and undemanding plant like C. Wendtii shouldn't be showing iron deficiencies.

Second, if I did start dosing magnesium, should I aim to match the amount I would be getting if I was using CSM+B? Or should I contact my water company to find out how much magnesium is already in the water and try to aim for an 'ideal' level?

Third (sorry this is a bit unrelated)... Since I was at the store I also picked up calcium nitrate (CaNO3). I don't think I need this necessarily, but it was cheap and at least I have it now should I ever need it for whatever the reason. 

If I was to start dosing CaNO3 for calcium, should I reduce my KNO3 dosage and use KSO4 to compensate for the potassium? Or am I missing something

The guaranteed analysis of my trace ferts:
Fe 7%
B 1.3%
Mn 2%
Zn 0.4%
Cu 0.1%
Mo 0.06%

(btw my magnesium source would be MgSO4, and if you don't mind, I use a 0.01g scale to measure my doses, so teaspoon measurements don't mean that much to me, sorry )


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## davemonkey (Mar 29, 2008)

It could be Magnesium. A couple grams or so of MgSO4 and you'd soon find out. Have you tried punching the numbers into the Fertilator? 

Also, be careful about dosing too much Mg. Mg and Calcium need to be in a balance of sorts, or you'll get too much of one and not enough of the other. Plants will consume all the available Mg in lieu of Calcium, even though it may be available, and you'd end up with Ca def. symptoms.


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## Skizhx (Oct 12, 2010)

See that's what I was worried about... Perhaps it would be best if I tried to duplicate the results I would get from CMS+B rather than aiming for what's deemed to be 'ideal' levels...

I use Nutri-Calc instead of the fertilator. It tells me 1/2 tsp. Which is useless to me, because as mentioned... I use a scale, not a spoon.

It also gives me a different recommended dose of KNO3 from Tom Barr's recommendations.

Quite honestly, I don't trust the software other people have made to calculate this stuff. At least not entirely.

I realize that sometimes coders make assumptions in order to make their software more friendly to the end-user. I can't comment on the fertilator program, but a glaringly obvious example is how Nutri-Calc assumes you're using CSM+B, and only gives doses in tsp and not g's.

I know enough coding to write a program like this if I need it, so honestly once I get the math and nutrients requirements down I'll probably just write my own calculator for personal use. I know enough chemistry that I should be able to figure out the math equations... So as things are now, I'm mostly relying on my own pen and paper calculations and using nutri-calc, etc to help double-check my numbers. And of course I'm learning about plants and their requirements from books, and from these forums (as well as other sources) 

That's good to know about the Mg/Ca relationship though and sort of brings me back to the question of should I contact my water company to try and get precise readings or should I try to mimic what I would get from CSM+B? And also, sort of turns back to the question I asked about dosing CaNO3.

I understand that downoi is sensitive to micro-nutrients as well, and I would like to keep this plant in the future, so any information pertaining to this would be greatly appreciated.

Thanks for taking the time to reply, btw


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## barbarossa4122 (Dec 31, 2009)

I dose 1/2 teaspoon Epsom 3 times/week in my 30g and this gives me about 7ppm of Mg/week but, I also dose about 30ppm of Ca/week via CaCl2 or CaSo4. Hope this helps.
http://calc.petalphile.com/

http://www.barrreport.com/showthrea...-can-plants-use-in-a-week?highlight=magnesium
http://www.plantedtank.net/forums/f...s/123292-calcium-magnesium-ratio-4-1-1-a.html
http://www.barrreport.com/showthread.php/7589-Ca-Mg-and-Gh?highlight=magnesium


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## Skizhx (Oct 12, 2010)

great links, thanks!


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## Skizhx (Oct 12, 2010)

Ok, so I've read around those links and looked at my water supplier's analysis...

9.2mg/L Mg

34.7mg/L Ca

120mg/L hardness as CaCO3

When I test my water I get 9dGH total, 3dKH.

So it seems that my Ca and Mg are already pretty close to 4:1 ratio.

However it also seems that my Mg is well within desired levels (5-10ppm)...

Unless I'm mistaken...

Any feedback? What's your take on this, am I barking up the wrong tree?



















(Sorry about quality, but just so I'm not going on trying to describe something I could just as easily show)


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## Diana K (Dec 20, 2007)

Well, I think you have done all your homework. 
The tap water STARTS OFF with enough Ca and Mg. 

Do the plants use it up very fast? Does the GH stay stable in the tank? Have you tested the GH right before a water change? 

I could see a couple of things to try here:
Increase the individual fertilizers one at a time, test for 1-2 weeks, then revert to the original dosing and test something else. This would fine tune your dosing and rather than following a strict EI dosing you will make your own recipe. You might start with Mg, if you want. 
OR
Increase everything, and add Mg and Ca to maintain the proper ratio. Just like ramping up the EI system as if it were a larger tank.


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