Fertlizer calculation help please - The Planted Tank Forum
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post #1 of 4 (permalink) Old 05-14-2020, 09:44 AM Thread Starter
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Fertlizer calculation help please

Hi all, I need some help calculating the ppms for my mixed all in one dry fertilizer, liquid form. I dont currently have any plant deficiencies but I heard that lower nitrates bring the red colours out more in some plants, since my fertilizer is quite high in nitrates I want to try lower my dosage but Iam extremly confused of my calculations.
Ok so currently I dose the recommended levels of 10ml, says 12 just simplifying it here, for every 100 litres, my tank being 300litres, 3 times a week, so per week 310ml 3 =90ml, right?. On the pack it states 12 ml in 100 litres yields: 7.5ppm nitrate. So I Would multiple that by 3 = 22.5ppm per dose times 3 = 67.5ppm per week, right??
What Iam confused about is if I want to know how much 12ml in 300 litres yields, would I just divide the 7.5 ppm for 100 litre by 3 to get 2.5ppm from 12ml in 300 litres???
Here it became really confusing since if I go this way and lets say i want to dose 12.8ml per day 7 days which equals to the same total of 90ml per week, I would end up with only 17.5ppm of nitrates for the whole week.
So either I am really not calculating this right or I am missing something.
I will post a pic of the nutrients below, hopefully someone can clear this up for me. Thanks
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post #2 of 4 (permalink) Old 05-15-2020, 06:00 PM
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12 mL for every 100 L is the recommended dosage. A 12 mL dose raises the nitrate levels in 100 L of water by 7.5 ppm (according to what you stated).

If you have a 300 L aquarium, then if you follow the dosage, you would add 36 mL, which would still raise your nitrate level by 7.5 ppm (assuming you want the final nitrate concentration to remain constant).

If you only add 12 mL to 300 L of water, then the final nitrate concentration would be 2.5 ppm, as you have correctly calculated. This is because the final volume of the water in your aquarium is 3x more, effectively diluting the final nitrate concentration by three (i.e. 7.5 ppm / 3 = 2.5 ppm)

As for your confusion

Quote:
On the pack it states 12 ml in 100 litres yields: 7.5ppm nitrate. So I Would multiple that by 3 = 22.5ppm per dose times 3 = 67.5ppm per week, right??
This is wrong. You are failing to take into account that your final volume of water is 300 L. 12 mL into 300 L yields 2.5 ppm. If you add 36 mL into 300 L, your final concentration is still 7.5 ppm.

If you do 36 mL * 3 times per week = 108 mL, then you would be adding 22.5 ppm of nitrates into your aquarium per week, assuming no uptake.
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post #3 of 4 (permalink) Old 05-16-2020, 10:21 AM Thread Starter
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Quote:
Originally Posted by Darkblade48 View Post
12 mL for every 100 L is the recommended dosage. A 12 mL dose raises the nitrate levels in 100 L of water by 7.5 ppm (according to what you stated).

If you have a 300 L aquarium, then if you follow the dosage, you would add 36 mL, which would still raise your nitrate level by 7.5 ppm (assuming you want the final nitrate concentration to remain constant).

If you only add 12 mL to 300 L of water, then the final nitrate concentration would be 2.5 ppm, as you have correctly calculated. This is because the final volume of the water in your aquarium is 3x more, effectively diluting the final nitrate concentration by three (i.e. 7.5 ppm / 3 = 2.5 ppm)

As for your confusion

Quote:
On the pack it states 12 ml in 100 litres yields: 7.5ppm nitrate. So I Would multiple that by 3 = 22.5ppm per dose times 3 = 67.5ppm per week, right??
This is wrong. You are failing to take into account that your final volume of water is 300 L. 12 mL into 300 L yields 2.5 ppm. If you add 36 mL into 300 L, your final concentration is still 7.5 ppm.

If you do 36 mL * 3 times per week = 108 mL, then you would be adding 22.5 ppm of nitrates into your aquarium per week, assuming no uptake.
Hi @Darkblade48, thank you for clearing that up for me! Never thought that's how it worked. My test kit for nitrate is like really red so Ithought I had more than 50ppm of nitrates. Thanks again
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post #4 of 4 (permalink) Old 05-18-2020, 02:32 AM
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Quote:
Originally Posted by Pascal View Post
Hi @Darkblade48, thank you for clearing that up for me! Never thought that's how it worked. My test kit for nitrate is like really red so Ithought I had more than 50ppm of nitrates. Thanks again
It is possible that your nitrates are really that high, but it's easy to test (just use distilled water and prepare some solutions of known concentrations).


Also, if you are using the API nitrate test kit (and any, really), you really have to make sure you shake the reagents very well. Otherwise, you could get erroneous readings.
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