DIY Phosphate Dosing Recipe

[Miami Reef]

@Miami Reef do you know if there's any place to get this stuff in person so I don't have to wait for shipping?

It will be difficult to source it in person. If you are in a rush, picking up Neophos is good idea. Both work. Neophos might be a bit more expensive by weight, but both get the job done.

 

[Reefer1978]

It will be difficult to source it in person. If you are in a rush, picking up Neophos is good idea. Both work. Neophos might be a bit more expensive by weight, but both get the job done.

Picked up some Neophos for now (ohh boy they changed labels over the years, 1.2ppm > 0.025ppm > 0.05ppm), and ordered some chemicals for the future. Thanks bud!!

 

[Miami Reef]

Picked up some Neophos for now (ohh boy they changed labels over the years, 1.2ppm > 0.025ppm > 0.05ppm), and ordered some chemicals for the future. Thanks bud!!

Of course.

 

[EnterName]

As this thread is limited to the use of "Sodium phosphate dibasic", I though I would provide recipes for various phosphate sources (and their different available hydrates), so you can use whatever is available to you.

To increase phosphate (PO₄) by 0.01mg/L in a 100L tank, we would need a total of 1mg PO₄ (= 100L ⋅ 0.01mg/L). A stock solution concentrated enough, so 1mL contains said 1mg PO₄ requires 1g PO₄ per liter stock solution (1mg/mL = 1,000mg/L = 1g/L). Down below you will find a few tables which will tell you how much of a specific salt contains 1g PO₄ so you can create your own stock solutions.

• If you want to increase PO₄ by 0.02mg/L instead of 0.01mg/L for every 1mL of stock solution added (like the original recipe from @Miami Reef suggested), you can simply multiply the values by 2.
• You can also make a stock solution fit your tank's size by further multiplying your tank's volume (in liter) divided by 100. Of course each salt has a limited solubility so you can't concentrate it indefinetly, but I think you can go to up to like 50 times the concentration even for the least soluble salt in the table.

Example 1:
I want to create 1L of stock solution which increases PO₄ by 0.01mg/L for every mL I add per 100L of tank volume. For monosodium phosphate dihydrate (NaH₂PO₄ ⋅ 2H₂O) this would require dissolving 1.64g in approx. 1L RO/DI. For trisodium phosphate dodecahydrate (Na₃PO₄ ⋅ 12H₂O) this would require 4.00g in approx 1L RO/DI.

Example 2:
I want to create 1L of stock solution which increases PO₄ by 0.01mg/L for every mL I add to my 625L tank.
For trisodium phosphate hexahydrate (Na₃PO₄ ⋅ 6H₂O) this would require 2.86g ⋅ 6.25 ≈ 17.88g to be dissolved in 1L RO/DI. For monosodium phosphate monohydrate (NaH₂PO₄ ⋅ H₂O) this would require 1.45g ⋅ 6.25 ≈ 9.06g to be dissolved in 1L RO/DI.

Notes:

• Weighing a few grams precisely isn't very easy, so you might want to create 10L instead of 1L of stock solution. Alternatively you can create a 10 times more concentrated solution and then use 10% of it to create the stock solution you actually need.
• I personally prefer using more dilute solutions so it can be dosed over time instead of dropping a phosphate nuke into my tank all at once.
• Adding theoretical 0.01mg/L to your tank will most likely not result in a 0.01mg/L increase as phosphates will fall out of solution, get consumed by algae and corals (especially when you currently have a phosphate limited system), or will be adsorbed by rocks, substrate, and bacteria.

Still haven't found your phosphate salt?
There are more phosphate salts which you could use, like ammonium phosphates and potassium phosphates, but these will increase ammonium & ammonia or potassium and therefore might be less suitable for your tank or for increasing phosphates in the long run without overdosing something else. If you want, I can add them as well but this will require some additional effort to make clear how much ammonia/potassium is added to the tank and what the caveats are.

Sources:
I used molar masses from Sigma Aldrich, CAS (Common Chemistry), and Carl Roth to come up with these values. However, mistakes happen and I would appreaciate someone double checking the numbers. It's fairly simple as you just need to divide the molar mass of the used salt by the molar mass of phosphate (≈ 94.97g/mol) and should end up with a number very close to the one from the posted table.

 

[Randy Holmes-Farley]

Thanks for posting these. :)

I do think that folks don’t need to get too crazy with exacting calculations since an unknown but potentially large fraction of a dose may get bound to rock and sand and won’t show up anyway.

 

[EnterName]

Thanks for posting these. :)

I do think that folks don’t need to get too crazy with exacting calculations since an unknown but potentially large fraction of a dose may get bound to rock and sand and won’t show up anyway.

Yeah, you are right

I know I tend to go a little bit overboard with trying to be as precise as possible. Most people don't know their actual net tank volume very precisely (myself included), nor do they use highly pure chemicals or have access to actually well calibrated scales.

I will try to find my inner engineer and just say: "2g/L stock solution, regardless of the used reagent listed above will do."

 

[Bubule]

For help

For those looking for phosphate in Europe (Na₂HPO₄ 2 H₂O) , Amazon doesn't seem to offer it. I managed to find some here:

di-Sodium hydrogen phosphate dihydrate CAS 10028-24-7

buy di-Sodium hydrogen phosphate dihydrate CAS 10028-24-7 ? di-Sodium hydrogen phosphate of the highest quality, always with volume discount!

www.laboratoriumdiscounter.nl

(177.99 g / mol)

And same dealer for Ammonium Bicarbonate (NH₄)HCO3) :

Want to buy food grade ammonium bicarbonate (CAS: 1066-33-7)?

Want to buy ammonium bicarbonate (CAS: 1066-33-7)? Laboratory discounter offers food grade ammonium bicarbonate for a friendly price! Shipped fast!

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[Bubule]

Mistake

 

[Bubule]

I'm not sure of myself...

With NA2HPO4-2H2O , molar mass is 177.99 g/mol

(2H2O : Water weight : 2 x 18.015 = 36.03). So 36.03 of water weight + 177.99 = 214.02 total.

With Po4 weight at 94.971, Po4 in NA2HPO4-2H2O is 94.971/214.02 = 44.37% (1g of powder = 0.44g of PO4).
If I prepare 1L with 1g of powder I obtain 0.44g/L

So to have 1g of Po4 /L or 1ppm/ml, I need to add 2.27g of powder per liter. Like this, my solution therefore contains 0.001 g/ml of PO4. Is that correct ?

Now, if I whant to raise my tank (1 200 L) of 0.01 ppm, I need to put 12 mg of Po4. So, 12 ml of my solution (2.27g powder/liter).

I hope haven't made mistake. Tell me

 

[EnterName]

I'm not sure of myself...

With NA2HPO4-2H2O , molar mass is 177.99 g/mol

(2H2O : Water weight : 2 x 18.015 = 36.03). So 36.03 of water weight + 177.99 = 214.02 total.

With Po4 weight at 94.971, Po4 in NA2HPO4-2H2O is 94.971/214.02 = 44.37% (1g of powder = 0.44g of PO4).
If I prepare 1L with 1g of powder I obtain 0.44g/L

So to have 1g of Po4 /L or 1ppm/ml, I need to add 2.27g of powder per liter. Like this, my solution therefore contains 0.001 g/ml of PO4. Is that correct ?

Now, if I whant to raise my tank (1 200 L) of 0.01 ppm, I need to put 12 mg of Po4. So, 12 ml of my solution (2.27g powder/liter).

I hope haven't made mistake. Tell me

The molar mass of Na₂HPO₄ ⋅ 2H₂O (the dihydrate form) is 177.99g/mol. This already includes the 2 H2O molecules. The anhydrate (Na₂HPO₄) has a molar mass of 141.96g/mol. Together with 2 H₂O (36.03g/mol) you get to 177.99g/mol:

141.96g/mol + 2 ⋅ 18.015g/mol ≈ 177.99g/mol

(Molar mass taken from Wikipedia)
​

Phosphate (PO₄) has a molar mass of roughly 94.97g/mol (just as you said), so it makes up roughly 53.36% of Na₂HPO₄ ⋅ 2H₂O's mass:

94.97g/mol / 177.99g/mol ≈ 53.36%​

Which means we can simply scale it up to 1g:

1g / 53.36% = 1g / 0.5336 ≈ 1.87g.
​

So 1.87g (Na₂HPO₄ ⋅ 2H₂O) contains 1g Phosphate, as 53.36% of 1.87g are roughly 1g PO₄.

For 1200L you would need to dissolve 22.44g per L stock solution.

(1200L / 100L) ⋅ 1.87g = 12 ⋅ 1.87g = 22.44g​

This way each liter stock solution contains 12g PO₄ and 1mL contains 0.012g = 12mg, so diluted over 1200L you get a 0.01µg/L PO₄ boost when dosing 1mL of the stock solution.

 

[Bubule]

Thanks a lot for your help and corrections. I mistakenly thought that the mass of water needed to be subtracted. For sure, I’m not a chemist !

In my case, I prefer introduce more volume with my dosing pumps in order to maintain sufficient accuracy with my old equipments (Grotech, Aquamedic). Below 5ml/injection they are not accurate. So, if I prepare my solution with 1mg/ml, I can introduce 12ml/injection (for 1 200 L).
As I imagine several doses per day will be needed, it should be more accurate.

For that, if I have understand correctly, i just need to dose 1.87g of powder in 1 liter RODI water.

Franck

 

[EnterName]

Thanks a lot for your help and corrections. I mistakenly thought that the mass of water needed to be subtracted. For sure, I’m not a chemist !

In my case, I prefer introduce more volume with my dosing pumps in order to maintain sufficient accuracy with my old equipments (Grotech, Aquamedic). Below 5ml/injection they are not accurate. So, if I prepare my solution with 1mg/ml, I can introduce 12ml/injection (for 1 200 L).
As I imagine several doses per day will be needed, it should be more accurate.

For that, if I have understand correctly, i just need to dose 1.87g of powder in 1 liter RODI water.

Franck

Yes, it makes sense to use more dilute solutions.

You can also prepare 1L with 18.7g (which is easier and more precise to weigh) to create a strong stock solution, which can be used to prepare a total of 10L of 1.87g/L stock solution.

Simply take 100mL of the strong solution and fill up to 1L with RO/DI which gives 1.87g/L.

Note that the used chemical will never be 100% pure and the scales used at home aren't perfect either, as well as measuring cups, so it won't really matter if it's 1.87g or simply 2g. During phosphate dosing you need to measure frequently anyway.

 

[Bubule]

Note that the used chemical will never be 100% pure and the scales used at home aren't perfect either, as well as measuring cups, so it won't really matter if it's 1.87g or simply 2g. During phosphate dosing you need to measure frequently anyway

Yes, but anyway, the daily volume will be determined by the concentration measured inside the tank. Therefore, regardless of the solution dosage, the daily injected volume will be adjusted according to Po4 level in the tank. So, in case of error in the preparation, it will be compensated for.

 

[HOLYREEFER]

I found my answer

 

[EnterName]

Will ATO with kalk causes problems for dosing sodium phosphate?

Just to be safe you could dose them at different spots in your tank or at different times. The locally elevated pH caused by Kalkwasser dosing might cause phosphate precipitation. In theory a lot of this precipitate should go back into solution over time, but this process might be slow and make the results unpredictable.

Edit:

I found my answer

Then share it with the community so we can learn :)