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

JoshP12

Member
Joined
8 Dec 2019
Messages
1,056
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
 
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.
 
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
 
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