Miracle Gro dosing for low tec

[jaisol]

I want to make a concentrated solution, that I can dose at the rate of 1ml fert to 10l of water, once a week.
I just want to improve my plant growth & I have a lot of miracle gro. There are no fish in the tanks, and my water is soft. ph7.1 (Darrel told me its soft)
I have tried to calculate this myself and came up with about 25g per l
I then tried chat gpt .. first answer was for 2.4kg, then told it that the ans seamed wrong & it told me 0.24g.
I used 10ppm N as the target, not sure if this is the correct target for low tech.
The fert is 24-3.5-13.3 with micros
link to label

https://www.lovethegarden.com/sites/default/files/content/products/documents/pack_label/UK_016922_MG_PL.pdf

 

[MichaelJ]

Hello @jaisol, I am not familiar with the usage of this product for growing aquatic plants and I don't know if the fertilizer declaration is based on the recommended dilution or not... Assuming its before the recommended dilution, the total amount of Nitrogen (N) in the compound is 24% so to target a reasonable 1 - 2 ppm of N in 10 liter of water weekly, you would dose between 40 milligrams and 80 milligrams (thats 0.08 grams).

I used 10ppm N as the target, not sure if this is the correct target for low tech.

On a weekly basis in a low tech tank 10 ppm of N would be over the top! Like eating this for dinner every day:

Cheers,
Michael

 

[jaisol]

Many thanks ]MichaelJ, I now know were my decimal point should be when I calculate it & what is a reasonable level is for low tech (1-2ppm).
Miracle Gro is not an aquatic plant fertilizer, it's a general garden fert, however I have a lot of it, and I figure some of that is better than nothing at all for my plants in a holding tank. I'm aware its not really suitable for aquatic use.

 

[dw1305]

Hi all,

Miracle Gro is not an aquatic plant fertilizer, it's a general garden fert, however I have a lot of it, and I figure some of that is better than nothing at all for my plants in a holding tank. I'm aware its not really suitable for aquatic use.

I've <"used it">. I'll do the calculation, but honestly a <"slosh of pale blue solution"> is the way forward.

that I can dose at the rate of 1ml fert to 10l of water, once a week.

Assuming its before the recommended dilution, the total amount of Nitrogen (N) in the compound is 24% so to target a reasonable 1 - 2 ppm of N in 10 liter of water weekly, you would dose between 40 milligrams and 80 milligrams (thats 0.08 grams).

Serial dilution is your friend here. We have 80 milligrams per 10 litres or 8 milligrams per litre Miracle-Gro and milligrams per litre is equivalent to ppm. Now we are just in the <"powers of ten">:

Calculation
One gram of Miracle-Gro supplies 240 mg of nitrogen (N) (that is the 24%) and 240 / 80 = 3, so one gram supplies enough N for 30 litres and a 1/3 of a gram enough for 10 litres.

So we need to make sure that our 1 mL (cm3) of Miracle-Gro stock solution contains 0.33 grams of Miracle-Gro. If we made a 100 cm3 stock up we would need to start with 33g of Miracle-Gro.

I'm guessing that is somewhere near the solubility limit, so I'd probably dose 5 mL*, which would mean that you need to add 33g of Miracle Gro and then make that up to 500 mL with DI, RO or rainwater.

* By that I really mean <"tip in a fairly random amount">.

cheers Darrel

 

[MichaelJ]

Serial dilution is your friend here. We have 80 milligrams per 10 litres or 8 milligrams per litre Miracle-Gro and milligrams per litre is equivalent to ppm. Now we are just in the <"powers of ten">:

I bought an expensive milligram scale to avoid all that ... but you are of course right - if you don't have the equipment serial dilution is the only way.

Calculation
One gram of Miracle-Gro supplies 240 mg of nitrogen (N) (that is the 24%) and 240 / 80 = 3, so one gram supplies enough N for 30 litres and a 1/3 of a gram enough for 10 litres.

So we need to make sure that our 1 mL (cm3) of Miracle-Gro stock solution contains 0.33 grams of Miracle-Gro. If we made a 100 cm3 stock up we would need to start with 33g of Miracle-Gro.

I'm guessing that is somewhere near the solubility limit, so I'd probably dose 5 mL*, which would mean that you need to add 33g of Miracle Gro and then make that up to 500 mL with DI, RO or rainwater.

* By that I really mean <"tip in a fairly random amount">.

I may have overlooked something, but 33 grams in a 500 ml solution to target 2 ppm with 5 ml per 10 liter looks off to me Darrel...

33 grams of MG diluted in 1 liter would make a solution that is is 33 * 0.24 * 1000 ppm = 7920 ppm N, but since we are only diluting in 500 ml the concentration be would twice that so 15840 ppm.

5 ml of a 15840 ppm solution diluted into 10 liters or 10,000 ml would yield (5 ml / 10000 ml * 15840) ppm = 7.92 ppm or a weekly dose of 7.92 of N per 10 liters.

If you wish to target 2 ppm with a 500 ml diluted solution where you dose 5 ml per 10 liter of water to reach 2 ppm of N, the correct solution should be:

5 ml / 10000 ml * x = 2 ppm. where x is 2 ppm / (5 ml / 10000 ml) = 4000 ppm. To reach 4000 ppm in a 500 ml container (x * 0.24 * 1000 * 2) = 4000 ppm, or x = 4000 / (0.24 * 1000 * 2) = 8.33 grams of MG,

8.333 grams * 0.24 * 1000 * 2 = 4000 ppm. 5 ml / 10000 ml * 4000 ppm = 2 ppm.

Cheers,
Michael

 

[dw1305]

Hi all,

I may have overlooked something, but 33 grams in a 500 ml solution to target 2 ppm with 5 ml per 10 liter looks off to me Darrel...

Yes, you are definitely right and I'm definitely wrong.

8.333 grams * 0.24 * 1000 * 2 = 4000 ppm. 5 ml / 10000 ml * 4000 ppm = 2 ppm.

Back to the drawing board for me I'm afraid.

That is why I use a slosh of pale blue Miracle-Gro, I can't add up, but my colour vision is fine.

cheers Darrel

 

[MichaelJ]

but my colour vision is fine.

Luckily we have a thread: What is the “Duckweed Index” all about?



Cheers,
Michael

 

[jaisol]

Many thanks Michael & Darrel.
So 8g into 1 litre, for a dose of 5ml per 10 litres of tank water, gives 2ppm.

With the above explanations & formulae I feel much more confident Thanks again

 

[MichaelJ]

So 8g into 1 litre

No, it is 8 grams into half a liter (500 ml.) otherwise you would have to dose 10 ml to maintain 2 ppm.

If we keep the 5 ml weekly constant - being that your 5 ml should be a 4000 ppm concentration of N, so when it's blended into the 10 liter of water it will contain 2 ppm of N: (5 / 10000) * 4000 = 2.

If you want to use a liter (1000 ml) container you would use 16.6 gram in order to maintain the concentration of 4000 ppm.

... or for any arbitrary sized container the calculation goes like this:

gramsMiracleGrow = 4000 ppm / (0.24 * 1000 * 1000 / mlSizeOfContainer)

The 0.24 being the fractional part ( 24% /100) of Miracle Grow that contains Nitrogen.

Example 1: If your using a 1 liter container:

4000 / (0.24 * 1000 * 1000 / 1000) = 16.6 gram

Example 2: If your using a 250 ml container:

4000 / (0.24 * 1000 * 1000 / 250) = 4.16 gram

for a dose of 5ml per 10 litres of tank water, gives 2ppm.

Yes. And depending on your plant mass and other conditions, if plants looks like they need a bit more, you just dose a bit more ... Assuming your color vision is fine - see more on this thread: leaf colour chart.


Hope all this helps!

Cheers,
Michael