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Magnesium in tap water

dw1305

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Hi all,
@dw1305 So for folks like myself living in the NE should we be adding up the Mg. in our tap water?

My water company reports an average of 5mg/L Mg. So after a 50% WC that would add 2.5ppm Mg so therefore is all this Mg. available to plants ? If so should we therefore adjust our dosing of MgSO4.7H2O to reach our target Mg ppm

e.g. So after a 50% WC in 500L tank we have added 2.5ppm Mg. Then if we add 5 teaspoons of Epsom salts(MgSO4.7H2O) to tank which yields 5ppm Mg. In a 500L tank we have 7.5ppm Mg. with the WC and the salts added
It should be plant available, how much the plants take up is really a numbers game.

If you have hard water adding some more magnesium isn’t going to hurt. You could have limestones which naturally supply a lot more Mg++ ions than you are going to add.

When you have a lot of Ca++ ions the next “taxi” on the rank is much more likely to be a Ca++ ion, rather than a Mg++ ion, which is why people have talked about the Ca:Mg ratio, rather than just ppm values.

Cheers Darrel
 
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@Zeus. This is what I'm trying to get a verdict on but also the CA/ mg/ K relationship and if the ratios are indeed important to counter the high CA. My tap water has 121.5mg/l CA and 8mg/l MG and the 3:1 ratio I've had to add 8tsp of MGSO4 to a 125ltr tank? MG has no I'll affects on livestock etc so I've just jumped in and added it, its the second week and my plants seem abit greener I must say but I was having a K defiency and also added K2SO4 so it could be this also.
 

Zeus.

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When you have a lot of Ca++ ions the next “taxi” on the rank is much more likely to be a Ca++ ion, rather than a Mg++ ion, which is why people have talked about the Ca:Mg ratio, rather than just ppm values.

:banghead::banghead::banghead:

So reminds me of the Rime of the Ancient Mariner -water water everywhere and not a drop to drink. This and my issues are starting to make a lot of sense to me, as Mg. deficiency looks very much like Fe deficiency - thinks it is as Mg plays a part in the synthesis of Chlorophyll. hence pale leaves dark veins.

This is what I'm trying to get a verdict on but also the CA/ mg/ K relationship and if the ratios are indeed important to counter the high CA.

Yes OFC

Only had time for a quick read after the penny has dropped, but dumpped 100g of MgSO4.7H2O in 500l tank this morning.

How did you determine the K deficiency?

Think it may have something to do with the Ca:Mg:K ratio !!!! only had a quick google ATM
 
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Hi @Craig Matthews

How did you determine the K deficiency? Was it by measurement or by observation?

JPC[/QUOTE
My hygrohila 53b and hygrohila Compacta started gaining many holes in old leaves outlined bye black,yellow colouring and the growth slowed rapidly until it didn't grow at all then staghorn crept in. I tried adding more kno3 and kh2po4 but it wasn't working and I'm guessing because the extra nitrates and phosphate was also accelerating growth so the ratio was always at the end of the tunnel now I've started adding k2so4 so hopefully I'm on to a winner. I have noticed that staghorn has disappeared but again I've also blacked my tank out during lights off as it was getting hit bye natural light a little. So I've done the classic to many remedies at once to know for sure the cause but the holes in leaves was a sure sighn. I also get new growth basically green but transparent in my hygrohila compact. Its early days adding the k2so4 and trying the 3:1 CA/mg ratio so I'll give it a few weeks and report back.
My tap water has 121.5mgl CA and 8mgl MG.
So 50% water change leaves 4mgl mg.
I need to make 36mgl in mg so I add 8 TSP to get the 3:1 ratio and I now add 30ppm per week k so that a ratio of 1:1 although I add this in 3 doses of 10ppm which would mean the 1:1 mg/k ratio is only at the end of the week before water change. So many variables trial and error I think.
 
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I also discovered that my EI mix method that comes with Aquariam plant food UK salts has a a guide of adding...
500ml water
4 TSP kno3
1 TSP kh2po4
6 TSP of mg.
This mix only gave me 15ppm of k per week. 5.5ppm per dose and trusty Clive's ei salts thread recommends 30ppm per week with 20ppm of nitrate and 3ppm of po4 per week.
 
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Hi @Craig Matthews

How did you determine the K deficiency? Was it by measurement or by observation?

JPC
Its also worth considering that K is a hierarchy to magnesium, iron etc so my plant symptoms was probably a mixture of many as they probably was not using inferior nutrients and as @dw1305 stated with a high CA content the next taxi will probably be a CA ion and my ratios was all over the place.
 

jaypeecee

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Hi @Craig Matthews

It looks like I'm being a bit thick here. In post #42 above, you said "its the second week and my plants seem abit greener I must say but I was having a K defiency and also added K2SO4 so it could be this also". How did you know that you had a potassium deficiency?

JPC
 
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Because I was getting lots and lots of holes in older leafs, I had a mass of leafs dropping, growing stopped and plants were pale. I read up on the ratios and dosed accordingly. I checked my fertilising regime and found that in my mixes I was only adding 15ppm of pottasium per week and it should be 30ppm per week.
 

jaypeecee

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Because I was getting lots and lots of holes in older leafs, I had a mass of leafs dropping, growing stopped and plants were pale. I read up on the ratios and dosed accordingly. I checked my fertilising regime and found that in my mixes I was only adding 15ppm of pottasium per week and it should be 30ppm per week.

Thanks for that. Now I understand. I am reminded of a similar thread to this one in which a member, @Thumper talked about the optimum ratio of Ca:Mg:K. Here it is:

https://www.ukaps.org/forum/threads/excess-potassium-problems.52216/page-3#post-580230

JPC
 
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No problem jpc That's a cool thread thanks, so from what thumper was saying if he has more magnesium than pottasium his plants would do ok but opposite way around then he would get problems and it all comes back to these ratio's. Hopefully we have some luck. Cheers
 

Zeus.

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Interesting read on Ca:Mg:K ratio

I also discovered that my EI mix method that comes with Aquariam plant food UK salts has a a guide of adding...
500ml water
4 TSP kno3
1 TSP kh2po4
6 TSP of mg.
This mix only gave me 15ppm of k per week. 5.5ppm per dose and trusty Clive's ei salts thread recommends 30ppm per week with 20ppm of nitrate and 3ppm of po4 per week.

APFUK is a starter guide which doesn't account for the various different water supplies and light intensities etc we use

Clive's EI salts is based on the N: P :K ratio of 7:1:10 which Tom Barr suggested. Plus his tank was very high light and very high [CO2]

Maybe we should be working backwards with our hard water- Calculate the Calcium we add each week with our WC, what Ca:Mg:K ratio we are going to use, then when we have our [Mg] per week we will have our target [K] and from there apply the N: P :K ratio of 7:1:10, kinda makes some sense in a way!!
 

Zeus.

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Maybe we should be working backwards with our hard water- Calculate the Calcium we add each week with our WC, what Ca:Mg:K ratio we are going to use, then when we have our [Mg] per week we will have our target [K] and from there apply the N: P :K ratio of 7:1:10

Then it follows on if we are after increasing our NO3 dose we will have to add more Ca and so on......
 
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Wow all this maths is way above my punching level, I'm getting a head ache lol. So at present my ca is 121.5, I've added mg to make 40ppm = 3:1 and my k at the end of a full dosing week would be 30ppm.
So I have a ratio of CA/mg/k 4:1:1.3 is my maths really that bad lol?
 

Zeus.

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Wow all this maths is way above my punching level, I'm getting a head ache lol. So at present my ca is 121.5, I've added mg to make 40ppm = 3:1 and my k at the end of a full dosing week would be 30ppm.

upload_2020-2-19_20-13-47.png
;)
 

Zeus.

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I'm getting a head ache lol

Then when you have your Ca : Mg : K ratio you have to work backwards to get the N:p:K ratio :crazy::crazy::crazy: even with a spreadsheet that does all the Calculations its being a PITA - the joys of hard water :lol:
 

Sammy Islam

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Interesting read on Ca:Mg:K ratio

APFUK is a starter guide which doesn't account for the various different water supplies and light intensities etc we use

Clive's EI salts is based on the N: P :K ratio of 7:1:10 which Tom Barr suggested. Plus his tank was very high light and very high [CO2]

Maybe we should be working backwards with our hard water- Calculate the Calcium we add each week with our WC, what Ca:Mg:K ratio we are going to use, then when we have our [Mg] per week we will have our target [K] and from there apply the N: P :K ratio of 7:1:10, kinda makes some sense in a way!!

Thanks for that, i've always wanted to know a rough number for my waters MG content. According to that calculator MG is about 16ppm if my CA is 130ppm. I usually add 2tsp mgso4 every water change to give me an extra 6 - 7ppm, might bump it up to 4tsp and observe.
 
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