Ca/Mg Dosing Ratio - The Planted Tank Forum
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post #1 of 22 (permalink) Old 10-18-2018, 08:32 PM Thread Starter
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Ca/Mg Dosing Ratio

Just purchased some Mangesium Sulfate/Calcium Sulfate, and need to make a batch 3:1 Ca/Mg. Just to make sure, for every tbsp of Mg, I add 3 tbsp of Ca. Correct? Sounds simple enough, just never mixed my own ferts before.
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post #2 of 22 (permalink) Old 10-18-2018, 10:35 PM
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Hi @Igor95,

Regrettably it is not quite that easy. Most GH Boosters are based upon Tom Barr's formula which is done by weight (pounds, ounces, grams) and not by volume (cups, tablespoons, etc).

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Barrs GH Booster contains magnesium sulfate (1 part), calcium sulfate (3 parts) and potassium sulfate (3 parts) by weight. It is an excellent water conditioner. If there are difficulties with solubility you can add a very small amount (1 tsp to 500 ml water) of cider vinegar to increase solubility
Most of use don't have kitchen scales but if you do they will work. If you do it by volume you should be fine with 3 parts calcium sulfate (CaSO4*2H2O) plus one part magnesium sulfate (Epsom Salt / MgSO4*7H2O) it should provide you with a mixture that will provide the following:

If dosed at one (1) level teaspoon per 8 gallons
Ca = 14.3 ppm
Mg = 3.32 ppm

and it will increase the hardness by 2.77 dGH

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post #3 of 22 (permalink) Old 10-19-2018, 12:48 AM
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Quote:
Originally Posted by Igor95 View Post
Just purchased some Mangesium Sulfate/Calcium Sulfate, and need to make a batch 3:1 Ca/Mg. Just to make sure, for every tbsp of Mg, I add 3 tbsp of Ca. Correct? Sounds simple enough, just never mixed my own ferts before.
A 3:1 ratio is about 2:1 Ca to Mg in actual dosing.

But better yet is to learn how to use either the Rotalabutterfly or Zorfox calculators. Will answer this question and many, many others.
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post #4 of 22 (permalink) Old 10-19-2018, 02:47 AM Thread Starter
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@Seattle_Aquarist, thank you. @Greggz, why does it come out to 2:1 in actual dosing? As for Rotalabutterfly calculators, I do use them. I just never used em to make my own macros/micros.
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post #5 of 22 (permalink) Old 10-19-2018, 02:56 AM
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Quote:
Originally Posted by Igor95 View Post
@Seattle_Aquarist, thank you. @Greggz, why does it come out to 2:1 in actual dosing? As for Rotalabutterfly calculators, I do use them. I just never used em to make my own macros/micros.
Simple.

100G tank.

Ca at 15 ppm is approximately 8 tsp.

Mg at 5 ppm is about 4 tsp.

3:1 PPM, 2:1 actual measurement.

Rough figures. Close enough for our purposes.

Understanding the calculators is worth the trouble. Just takes a little time and dedication, then makes perfect sense.


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post #6 of 22 (permalink) Old 10-19-2018, 03:00 AM Thread Starter
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Ahh, I see now. You meant it's 2:1 measurement wise. I'm playing with the calculators right now, but I think I got it for the most part. I can mix it at the given ratios, the problem I'm trying to understand now is the dosing after it's mixed. What would the dosages look like for a 75G if I do it at 3:1 ratio. That's all that confuses me at this point.
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post #7 of 22 (permalink) Old 10-19-2018, 05:30 AM
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On the calculator down at the bottom where it says "calculating for" change EI to "dose to reach a target"

Enter 15 ppm for Ca -or whatever ppm you're trying to hit - and 5 for mg
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post #8 of 22 (permalink) Old 10-19-2018, 12:48 PM
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Depends on the source. My CaSO4 is a power, my MgSO4 is granular. My dosing is roughly 1:1 of each by volume, but it gives me the 3:1 ratio of actual Ca:Mg.

A $20 scale from amazon is worth every penny. Even without a scale, for our purposes getting roughly Ca and Mg to the right levels is fine with measuring spoons.
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post #9 of 22 (permalink) Old 10-19-2018, 03:00 PM
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how often do you dose MG and Ca?

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post #10 of 22 (permalink) Old 10-19-2018, 03:21 PM
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how often do you dose MG and Ca?
Most people dose once a week, right after doing a water change.

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post #11 of 22 (permalink) Old 10-19-2018, 04:16 PM Thread Starter
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I'm dosing GH Booster 3 tbsp after wc. My problem is that I'm adding too much K. With everything added, I'm getting close to 40K weekly. The tank isn't planted enough imo.
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post #12 of 22 (permalink) Old 10-19-2018, 04:23 PM
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Quote:
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I'm dosing GH Booster 3 tbsp after wc. My problem is that I'm adding too much K. With everything added, I'm getting close to 40K weekly. The tank isn't planted enough imo.
In my limited experience, you only get excess K if you don't have enough plant mass, like you suspect.

Especially if the K is from your GH booster. You might check your GH levels too, as they may be considerably higher than your tap water if you are seeing excess K.

So long as we're on the topic, is anyone recommending dosing these Ca/Mg ferts over just buying some GH booster product? I've had a container of Equilibrium that I've not finished for probably 4 years now, and it saves me the step of combining multiple macros. Though I can understand a desire to have complete control on your fert dosing.

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post #13 of 22 (permalink) Old 10-19-2018, 04:26 PM Thread Starter
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@Blacktetra, GH levels from tap are 2 along with KH. I have no test kit for K, but I'm positive I'm getting a lot of accumulative K since the plant mass isn't there to take it all in. That's why I'm trying to mix my own Ca/Mg mix.
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post #14 of 22 (permalink) Old 10-19-2018, 05:20 PM
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Quote:
Originally Posted by Blacktetra View Post
So long as we're on the topic, is anyone recommending dosing these Ca/Mg ferts over just buying some GH booster product?
Yes MgSO4 and CaSO4 are all you need. Every GH booster is basically a combination of those and K.

If you take it a step further and get a Ca test kit, you can get a good idea of your Mg and ratio based on your GH. Just saying tap could have lots of one, but little of the other, so you can dose more/less of each to get whatever ratio you are shooting for.
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post #15 of 22 (permalink) Old 10-19-2018, 06:41 PM
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Quote:
Originally Posted by Greggz View Post

If you take it a step further and get a Ca test kit, you can get a good idea of your Mg and ratio based on your GH. Just saying tap could have lots of one, but little of the other, so you can dose more/less of each to get whatever ratio you are shooting for.
Recommendations on a decent Ca test kit? I'm interested....

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