need help with Mg and Ca sulfate - The Planted Tank Forum
 
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post #1 of 10 (permalink) Old 07-20-2011, 12:17 AM Thread Starter
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need help with Mg and Ca sulfate

am switching to RO/DI water this week and i will be mixing 25% tap water with ro/di water, i want to know how you guys dose the Mg and Ca, how much you guys dose and how many times per week.

i want to dose good amount while keeping the GH/Kh at lower levels. should i dose 1 teaspoon of Ca and Mg 3x week? or 3 teaspoon 1x week?

does Ca and Mg stay in water forever or does it only last for couple of hours just like Iron does?

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post #2 of 10 (permalink) Old 07-20-2011, 03:32 AM
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Quote:
Originally Posted by happi View Post
am switching to RO/DI water this week and i will be mixing 25% tap water with ro/di water, i want to know how you guys dose the Mg and Ca, how much you guys dose and how many times per week.

i want to dose good amount while keeping the GH/Kh at lower levels. should i dose 1 teaspoon of Ca and Mg 3x week? or 3 teaspoon 1x week?

does Ca and Mg stay in water forever or does it only last for couple of hours just like Iron does?
The only way I know that Ca and Mg will precipitate out is if your ionic balance of your water is WAY off. It won't last forever since plants do absorb it, but it should be much more stable in water than iron. I had issues with my iron precipitating out with hard water. After switching to DPTA, I've had no issues.

Why do you want your GH to be low? As I understand it, plants don't really care about GH as much as KH... if I were using RO/DI water for my planted tanks, I would just add GH booster as per EI dosing... but I have no idea what you're trying to accomplish...
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post #3 of 10 (permalink) Old 08-01-2011, 05:41 AM Thread Starter
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i just wanted to keep the KH/GH low, even though GH isn't important to the plants.

my main question is now that how long Mg and Ca last in the water? do we have to dose these every day or once a week should be good enough?

i have a 50g high light tank, high co2 and 50% water change, EI dosing.
am adding 1tsp of Ca once a week with water change and 3tsp of Mg 3x week. am i doing it correctly.

i add 75% ro/di and 25% tap water and am sure my tap water have some Ca.

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post #4 of 10 (permalink) Old 08-01-2011, 11:47 PM
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Well GH is a usless number for doing planted aquarium. What you need to know is the ppm of Ca+2 and Mg+2 in your tap water. You would like the ratio of Ca+2/Mg+2 to be something like 2/1 - 5/1. and the amount of Mg+2 to be at least 10 ppm.

Dilute your tap water out to get something like I've described. It doesn't have to be exact.

This GH thing is very arcane and basically usless so be careful when you research this topic.

Once you get you Ca+2/Mg+2 in line you can add any acid or base to get the KH to what you need.

If you play with chemicals you should know some chemisty.
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post #5 of 10 (permalink) Old 08-02-2011, 09:49 PM Thread Starter
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Quote:
Originally Posted by happi View Post
i just wanted to keep the KH/GH low, even though GH isn't important to the plants.

my main question is now that how long Mg and Ca last in the water? do we have to dose these every day or once a week should be good enough?

i have a 50g high light tank, high co2 and 50% water change, EI dosing.
am adding 1tsp of Ca once a week with water change and 3tsp of Mg 3x week. am i doing it correctly.

i add 75% ro/di and 25% tap water and am sure my tap water have some Ca.
could anyone answer these questions.

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post #6 of 10 (permalink) Old 08-02-2011, 11:24 PM
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Quote:
Originally Posted by happi View Post
am switching to RO/DI water this week and i will be mixing 25% tap water with ro/di water, i want to know how you guys dose the Mg and Ca, how much you guys dose and how many times per week.

i want to dose good amount while keeping the GH/Kh at lower levels. should i dose 1 teaspoon of Ca and Mg 3x week? or 3 teaspoon 1x week?

does Ca and Mg stay in water forever or does it only last for couple of hours just like Iron does?
I thought I answered these but let me give a little more info.

Ca+2 and Mg+2 are generally stable in solution and last forever. (Unless there is a loss of CO2, which causes Ca+2 to drop out of solution).

If you are using tap water, this should be your total source of both Ca+2 and Mg+2. Hard water is the best source of these ions as they are in a stable state.

Find out how much Ca+2 and Mg+2 are in your city water (in ppm of Ca+2 and Mg+2). If the ratio is 5/1 through 2/1 just dilute it out with RO so that you have at least 10 ppm of Mg+2. This will result in “slightly soft” water when you test for GH, which is good for many fish and is OK for plants.
If the ratio is higher you need to add Mg+2. If it is lower you need to add Ca+2 (which is pretty rare).

If you are using a GH booster to get your RO right you probably are wasting your time unless the vendor specifies the amount of ppms of Ca+2 and Mg+2 per dose.

If you play with chemicals you should know some chemisty.
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post #7 of 10 (permalink) Old 08-02-2011, 11:31 PM Thread Starter
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Quote:
Originally Posted by ray-the-pilot View Post
I thought I answered these but let me give a little more info.

Ca+2 and Mg+2 are generally stable in solution and last forever. (Unless there is a loss of CO2, which causes Ca+2 to drop out of solution).

If you are using tap water, this should be your total source of both Ca+2 and Mg+2. Hard water is the best source of these ions as they are in a stable state.

Find out how much Ca+2 and Mg+2 are in your city water (in ppm of Ca+2 and Mg+2). If the ratio is 5/1 through 2/1 just dilute it out with RO so that you have at least 10 ppm of Mg+2. This will result in “slightly soft” water when you test for GH, which is good for many fish and is OK for plants.
If the ratio is higher you need to add Mg+2. If it is lower you need to add Ca+2 (which is pretty rare).

If you are using a GH booster to get your RO right you probably are wasting your time unless the vendor specifies the amount of ppms of Ca+2 and Mg+2 per dose.
much better answer, i tested my water while back for Ca and Mg, results were Ca 186ppm and Mg 0ppm.

i did not understand the part about Ca and Mg last forever unless co2 drop. are you saying TDS will fall lower if there is no co2 in the water.

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post #8 of 10 (permalink) Old 08-02-2011, 11:33 PM
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Quote:
Originally Posted by happi View Post
i just wanted to keep the KH/GH low, even though GH isn't important to the plants.

my main question is now that how long Mg and Ca last in the water? do we have to dose these every day or once a week should be good enough?

i have a 50g high light tank, high co2 and 50% water change, EI dosing.
am adding 1tsp of Ca once a week with water change and 3tsp of Mg 3x week. am i doing it correctly.

i add 75% ro/di and 25% tap water and am sure my tap water have some Ca.
Uptake wise from the plants, it's not likely one would need more than say 5-10ppm of Ca+ and 2=5ppm of Mg, I tend to add about 10ppm Ca and about the same as Mg, my tap has virtually no Mg, so I add a bit more of that relative to Ca.

For RO..........I doubt it matters much, I'd just add about 1/2 tsp of MgSO4 to each 10 Gal of make up water for the water changes with you 75/25 split, that's enough once a week.




Regards,
Tom Barr
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post #9 of 10 (permalink) Old 08-02-2011, 11:49 PM Thread Starter
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Quote:
Originally Posted by plantbrain View Post
Uptake wise from the plants, it's not likely one would need more than say 5-10ppm of Ca+ and 2=5ppm of Mg, I tend to add about 10ppm Ca and about the same as Mg, my tap has virtually no Mg, so I add a bit more of that relative to Ca.

For RO..........I doubt it matters much, I'd just add about 1/2 tsp of MgSO4 to each 10 Gal of make up water for the water changes with you 75/25 split, that's enough once a week.
thanks tom, i would add it once a week.

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post #10 of 10 (permalink) Old 08-03-2011, 12:03 AM
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much better answer, i tested my water while back for Ca and Mg, results were Ca 186ppm and Mg 0ppm.

i did not understand the part about Ca and Mg last forever unless co2 drop. are you saying TDS will fall lower if there is no co2 in the water.

Yes TDS will drop off, this is because of the [Ca+2] [CO2] relationship.
I'll make it simple:

CaHCO3 is readily soluble in water while CaCO3 is practically insoluble in water.
So

Ca(HCO3)2 à CaCO3 + H2O + CO2

If you lose CO2 TDS declines (This is the limestone cave process or the temporary hardness process)

If you play with chemicals you should know some chemisty.
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