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Discussion Starter · #1 ·
aside from sending them off to a lab, if I make my own liquid solution how can I get the number
an example would be flourish comp would have somethin on the side looking like this

magnesium............. .07%
maganese............... .03%
calcium................... .2%
FE iron.................... .15%

these are not the real numbers but this is the type of thing I am tryin to figure out the equation for gettin these numbers.
 

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Hey kinetic! Make up a batch of 1000 total grams of dry ferts. Each 10 grams would equal 1%. So to get .15% iron you would add 1.5 grams. Not very much. I think thats the idea? At work I mix up about 1000 pounds of dry ferts per week haha but we have a set formula.
 

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Discussion Starter · #3 ·
hey Dan,

where do you work? is it dry fert mixes for aquariums??

and the numbers I need are for liquid ferts... I am mixing 60 g potasium nitrate, 15 g potasium phosphate, 10 g ultimate GH boost from GLA, 8.5 g potasium sulfate, 6.5 g magnesium sulfate, into 1000 ml of water...

I realize that the water weighs approximately 1000 g however as I have checked another solution where someone from GLA gave the numbers it did not match just the simple formula of weights when added to water such as it calls for .872 g into 1000ml of water which going by weight would be 1000/.872 so it would be .0872% of mnso4, however it only has it listed as .04% of mn, this may have to do with the percentage of pure mn in mnso4.. however I do not know..
 

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Hey kinetic! Make up a batch of 1000 total grams of dry ferts. Each 10 grams would equal 1%. So to get .15% iron you would add 1.5 grams
That doesn't actually work because you are not adding nutrients in their elemental or pure form. Pretty much any nutrient you add will be bound up in salt form.

Use the periodic table and the empirical formula of the compound to determine the percentage of mass of the element you want in the salt you are using. Divide the mass of the element that you need in the mixture by the percentage composition of the element and you now know how much total mass you need to add of that particular salt.

For example, if you need 5 grams of calcium and the percentage of your salt that is calcium is 20%, then you would add 25 grams of that compound.

The easiest way to do this is to make the formula so that it easily divides into an even number of doses that you plan to use in your tank.

Lets say you are going to dissolve this into a 500mL flask of water, and you want to get 10 doses per mixture. You will need to add enough of the element to produce 10X the concentration you want to dose in your tank and then dose 50mL each time. If you want 10ppm or mg/L, in a 100 liter tank, then you will add 1 gram at each dose. You now know that you need 10 grams of that element to add to your solution. So if you were using the calcium example above, you need to add 50 grams. Do this relatively simple calculation for each nutrient.

Once you know what the total weight of a dose will be, you can multiply the formula by any amount to keep a dry mix handy.

Doing it this way prevents you from having to use a more complicated equation to determine the percentage without knowing what the mass of the final solution will be.

It's easier to figure out if you make the liquid volume of the container something evenly divisible by 10 also.

It's also better to put all of the dry salts into the flask, then fill with water to 500mL. Otherwise if you start with 500mL of water the total volume will increase when you add your dry mix.

Wow. This is so much easier to just do than it is to explain.

This is math that we learned in the fourth grade, it's just difficult for many people to apply to real world situations because they aren't accustomed to thinking in this way.

Pretty much all of our dry ferts will be hygroscopic also, meaning that they will contain a decent amount of water, forming pentahydrates and the like. This will have an affect on the weight of the dry fertilizer, lowering the percentage of the nutrient we want. When I do rough calculations, I just ignore this, as ultra precise measurement is totally unecessary for our purposes.

By the way, using this method, you can easily make your own clone of any commercial fertilizer you can buy, whether agricultural, aquatic, or hydroponic, using the ingredient list and the guaranteed analysis required to be printed on the bottle by the Department of Agriculture.
 

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Discussion Starter · #6 ·
thats awesome dan, I cut my teeth in growing plants with hyrdoponics.. I really enjoyed growing stuff and when I moved back to PA and got into tanks, adding plants has gone pretty overboard..

so do you grow anything emersed? I was thinking of doing this with some plants just to check out growth rate and possibly even setup something that looked like a beautifully scaped tank but without the water..

BTW I know I said about clubs up in this area, we have not gotten anything started but the club I go to in lancaster next month is having some very knowledgeable people coming from the Greater Washington area doing a presentation on plants and even having a scaping competition..
 

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An example:
Epsom salt, a common source of magnesium - MgSO4.7H2O

Each mole of this has a mass of 24 + 32 + 4x16 + 7 (2x1 + 16) = 246g. Of that 246g, only 24.3g are magnesium. So if you want a given amount of magnesium in a solution (lets say 0.2% or 2000 ppm, just as an example) you'd want 2 grams of magnesium in every liter of solution. To get that 2 grams, you'd need to add 246/24.3 times as much epsom salt to your solution. Conveniently, that comes out to be about 10 times as much, or 20g.

Here are stepwise instructions for what Sharkfood is saying.

For any given chemical MX, where M is the component you're adding:
1. Determine the percentage you want your stock solution to have of M.

2. Find the mass of MX using the periodic table and taking care to check to see if it is hydrated.

3. Find the mass of M in a mole of MX. If it is a case where there is more than one atom or polyatomic ion of M present per molecule, count all of the atoms/ions of M present.

4. Multiply your desired concentration by 10 if it is a percent, or divide it by 1000 if it is in ppm. This is the number of grams of M that you want in one liter of solution.

5. Multiply this quantity by the mass of MX determined in step 3 and divide it by the mass of M determined in step 4. This is the number of grams of MX you would need to dissolve in enough water to make 1 liter of solution to get the desired concentration.

6. If you are not making 1 liter of solution, multiply the value from 5 by the number of milliliters of solution you are making and divide by 1000 to determine your particular needs.
 
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