Help me understand Ca/Mg amount vs. ppm - Page 3 - The Planted Tank Forum
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post #31 of 39 (permalink) Old 07-25-2020, 03:21 AM Thread Starter
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MgSO4.7H2O
Means 7 molecules of water are bound to the MgSO4.
Practical meaning is it weighs 7 water molecules more than MgSO4 non-hydrated.

You need to account for the water weight to determine the actual amount of Mg..

Maybe this was mentioned before..
120.366 g/mol MgSO4
246.47 g/mol MgSO4 . 7H2O

Hydrated form has 1/2 the magnesium as the non-hydrated form on a gram to gram basis approx..

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Magnesium sulfate is a chemical compound, a salt with the formula MgSO
4, consisting of magnesium cations Mg2+
(20.19% by mass)
1g MgSO4 = .2019G Mg
.1008g Mg in a gram of MgSO4.7H2O (Epsom salt)

48.8% would be more exact than 50%

IF I remember my chemistry right.. Big if.


100.8 mg/gram of epsom salts
1 gram in 36gal (est of 40gal tank) 136.3L
100.8/136.3 = 0.740ppm..
To ADD 5ppm = 6.75 Grams.. Nobody should use spoons.. :-)
Checked calcs here..
https://www.flowgrow.de/db/calculato...5Bdose%5D=6.75

https://aquariumscience.org/index.ph...-in-the-water/

I know all a we bit o/t but a bit bored today..
Boy, this is getting complicated. Isn’t the idea behind EI dosing to dose a set amount per week followed by a 50% water change, and the levels will eventually accumulate to where they need to be? And if EI supposedly doses in excess, then why is K so lacking?

If I dose the recommended NPK (1/8 tsp, 1/32 tsp, 1/32 tsp) three times per week, won’t my potassium level eventually reach what it needs to be? Do I really need to double my K dosing, and if so, why does the EI method use so little K? Is it primarily based on the Ca and Mg being dosed? Users should tweak the standard numbers for their particular Ca/Mg concentration?

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post #32 of 39 (permalink) Old 08-02-2020, 03:17 AM Thread Starter
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Here's the article I'm referring to (last sentence in "the ratio" section): https://www.aquasabi.com/aquascaping...-and-magnesium
I don't think that I could trust that site. Ca can interfere with K uptake, which would make me concerned that having so much Ca, relative to K, might starve the plants for K.
Just noticed the same website says PO4 should be 0.1 to 1 ppm and iron 0.05 to 0.1 ppm. Seems awfully low. I thought PO4 should be more like 3 or 4 ppm and iron 0.5 ppm or higher.

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post #33 of 39 (permalink) Old 08-03-2020, 02:13 AM
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Just noticed the same website says PO4 should be 0.1 to 1 ppm and iron 0.05 to 0.1 ppm. Seems awfully low. I thought PO4 should be more like 3 or 4 ppm and iron 0.5 ppm or higher.
PO4 can range from .1 to 10ppm, depending upon the setup. It can also be used to slow growth without harming the plants (trying to do this in other ways, e.g.; by cutting CO2 can harm plants). In general, I would target between 1-5 ppm and also try to make it close to a 10:1 ratio with NO3:PO4, but prioritizing a minimum PO4 level. If you have GSA problems, push PO4 to 5ppm, or higher. In my own tank, I target 3-4ppm, but it can drift higher before the w/c. All of my PO4 is provided by my fish. I wouldn’t want to go below 1ppm as this could risk running it out without realizing it.

Iron is mostly a function of chelation type and plant needs (some like a lot of iron). Example: I dose .19ppm daily, but Dwarf Sag likes a lot of iron and I use gluconated iron (Seachem Flourish Iron), which is consumed rapidly by plants (within a half-hour). If I used something like DTPA iron, I would use a lower dose.

Note that my PO4 is a maintenance level, not a dosing level, while iron is a dosing level. When you say “iron 0.5 ppm or higher”, does that mean a maintenance level or a dosing level and, if dosing, what is the frequency?
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post #34 of 39 (permalink) Old 08-03-2020, 02:37 AM Thread Starter
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Just noticed the same website says PO4 should be 0.1 to 1 ppm and iron 0.05 to 0.1 ppm. Seems awfully low. I thought PO4 should be more like 3 or 4 ppm and iron 0.5 ppm or higher.
PO4 can range from .1 to 10ppm, depending upon the setup. It can also be used to slow growth without harming the plants (trying to do this in other ways, e.g.; by cutting CO2 can harm plants). In general, I would target between 1-5 ppm and also try to make it close to a 10:1 ratio with NO3:PO4, but prioritizing a minimum PO4 level. If you have GSA problems, push PO4 to 5ppm, or higher. In my own tank, I target 3-4ppm, but it can drift higher before the w/c. All of my PO4 is provided by my fish. I wouldn’t want to go below 1ppm as this could risk running it out without realizing it.

Iron is mostly a function of chelation type and plant needs (some like a lot of iron). Example: I dose .19ppm daily, but Dwarf Sag likes a lot of iron and I use gluconated iron (Seachem Flourish Iron), which is consumed rapidly by plants (within a half-hour). If I used something like DTPA iron, I would use a lower dose.

Note that my PO4 is a maintenance level, not a dosing level, while iron is a dosing level. When you say “iron 0.5 ppm or higher”, does that mean a maintenance level or a dosing level and, if dosing, what is the frequency?
Maintenance level with respect to the iron. I've been adding 0.1 ppm per day of Fe gluconate 12.46% (GLA). I do get a bit of GSA on the glass. Last I measured, my PO4 was 4 to 5ppm in that tank. I EI dose my high tech 20 gal and use the same ferts for my 65 gallon but at about half the dose (because I don't want to do weekly water changes on two tanks).

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post #35 of 39 (permalink) Old 08-03-2020, 03:38 AM
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I've been adding 0.1 ppm per day of Fe gluconate 12.46% EDTA (by GLA) on top of 0.15 ppm of iron contained in the micros I add three times a week (weekly total of 1.15ppm).
I don't understand what you mean by "Fe gluconate 12.46% EDTA." Does GLA have a combination gluconate and EDTA offering?
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post #36 of 39 (permalink) Old 08-03-2020, 04:10 AM Thread Starter
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I've been adding 0.1 ppm per day of Fe gluconate 12.46% EDTA (by GLA) on top of 0.15 ppm of iron contained in the micros I add three times a week (weekly total of 1.15ppm).
I don't understand what you mean by "Fe gluconate 12.46% EDTA." Does GLA have a combination gluconate and EDTA offering?
Sorry, I got confused. The micros I am dosing have EDTA and DPTA iron. I am supplementing with the GLA Fe Gluconate.

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post #37 of 39 (permalink) Old 08-03-2020, 02:11 PM
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Sorry, I got confused. The micros I am dosing have EDTA and DPTA iron. I am supplementing with the GLA Fe Gluconate.
OK, that makes sense. You may not need the EDTA (it may not be providing iron in usable form). If your pH is generally above 6.0-6.5, the EDTA will begin to precipitate out and be unavailable to your plants. Beginning in that pH area and up into the pH 7.5 area is where the DTPA is better suited. Additionally, neither of these will work well if you have a high-end UV sterilizer (which is why I use gluconate exclusively).
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post #38 of 39 (permalink) Old 08-03-2020, 02:24 PM Thread Starter
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Sorry, I got confused. The micros I am dosing have EDTA and DPTA iron. I am supplementing with the GLA Fe Gluconate.
OK, that makes sense. You may not need the EDTA (it may not be providing iron in usable form). If your pH is generally above 6.0-6.5, the EDTA will begin to precipitate out and be unavailable to your plants. Beginning in that pH area and up into the pH 7.5 area is where the DTPA is better suited. Additionally, neither of these will work well if you have a high-end UV sterilizer (which is why I use gluconate exclusively).
I switched to the EDTA/DPTA micromix when I started injecting CO2, because my pH drops to about 6.7. I was using the Seachem iron for a while and noticed good results, so maybe I'll switch back to the DPTA.

I don't have a UV light in the 65 gallon, but I have one in my 20, which I disconnected last week actually.

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post #39 of 39 (permalink) Old 08-03-2020, 10:16 PM Thread Starter
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Sorry, I got confused. The micros I am dosing have EDTA and DPTA iron. I am supplementing with the GLA Fe Gluconate.
OK, that makes sense. You may not need the EDTA (it may not be providing iron in usable form). If your pH is generally above 6.0-6.5, the EDTA will begin to precipitate out and be unavailable to your plants. Beginning in that pH area and up into the pH 7.5 area is where the DTPA is better suited. Additionally, neither of these will work well if you have a high-end UV sterilizer (which is why I use gluconate exclusively).
Okay. I'll switch back to the DPTA and see what happens. I have a UV light on my 20 gal, which I recently turned off.

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