High Ca in tap water. How much Mg do you need to add?

JoshP12

Member
Joined
8 Dec 2019
Messages
406
Location
Canada
Hi all,

Subject line really. I am curious about some of you in the UK with hard water (I have soft where I live). If your hard water has LOTS of calcium and minimal Mg, then how much (if any) magnesium do you need to add to it to not show a magnesium deficiency?

It can be in a daily dose or in the water change water.

Much appreciated!
Josh
 

Witcher

Member
Joined
15 Jan 2020
Messages
275
Location
London
Hey Josh, if you're looking for straight answer with the numbers, then at 3ppm Mg I don't see any deficiencies (I keep this for approx 3 months so I'm sure it's enough).

More details if needed:
6ppm Ca (that's actually 2:1 Mg:Ca)
5ppm K

But obviously because high Ca (and hardness in general) in the tap I remineralize water from scratch either with RO or rain water - between 0-1kh (I'm actually still testing the levels due to certain plants) and 1.5-2dGH.

Previously when I kept plants suitable for my tap (approx 100ppm Ca) I was adding approx 25-30ppm Mg and approx 30K.
 

JoshP12

Member
Joined
8 Dec 2019
Messages
406
Location
Canada
Hey Josh, if you're looking for straight answer with the numbers, then at 3ppm Mg I don't see any deficiencies (I keep this for approx 3 months so I'm sure it's enough).

More details if needed:
6ppm Ca (that's actually 2:1 Mg:Ca)
5ppm K

But obviously because high Ca (and hardness in general) in the tap I remineralize water from scratch either with RO or rain water - between 0-1kh (I'm actually still testing the levels due to certain plants) and 1.5-2dGH.

Previously when I kept plants suitable for my tap (approx 100ppm Ca) I was adding approx 25-30ppm Mg and approx 30K.
Thanks so much!

I love this idea of rain water - I have read it over and over again - if its good enough for real fish, it must be good enough for me!

This is great info -- my recent experience with high K in my water causing issues has led me down this track. Your experience supports my hypothesis that you would need more mg to balance out the excess calcium.

In truth, I am trying to understand whether the relative concentrations (and this is as a result of Mulders) are equally as important as straight concentration. I think it is - but I wanted to get some actual data to see if I am completely misunderstanding or not.

Josh
 

Zeus.

Member
Joined
1 Oct 2016
Messages
3,109
Location
Yorkshire,UK
Tap water
Ca 141.5 ppm
Mg 5.5ppm

Toss about two teaspoons of MgSO4 and about six TSP of KSO4 in 500l straight after WC

Does it help ? Dunno only been doing it couple of months. But tank doesn't look worse 🤣
 

JoshP12

Member
Joined
8 Dec 2019
Messages
406
Location
Canada
Tap water
Ca 141.5 ppm
Mg 5.5ppm

Toss about two teaspoons of MgSO4 and about six TSP of KSO4 in 500l straight after WC

Does it help ? Dunno only been doing it couple of months. But tank doesn't look worse 🤣
It does! Thank you!
 
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