Dosing KH2PO4 without KNO3 and EI? - The Planted Tank Forum
Old 04-14-2016, 03:35 PM Thread Starter
Algae Grower

Join Date: Jan 2015
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Dosing KH2PO4 without KNO3 and EI?

Hi all,

I'm using this calculator to determine the quantities for my stock solutions for EI dosing:

https://www.thenutrientcompany.com/a...ei_calculator/

My tank is 32 gallons, dose volume is 30 mL, stock volume is 0.9 L and I'm dosing 6 days/week.

The calculator tells me that I should add 56g of KNO3 and 16G of KH2PO4 for the macro solution. The problem is that I think my fish are providing enough nitrates on their own, so I don't need to supplement my tank with additional nitrates.

If I just wanted to add potassium and phosphate with KH2PO4, how much would I add and how would you determine that? I imagine it should be more than 16g to make up for the missing volume of KNO3. On the other hand, is that missing volume so minute that the difference is irrelevant?

Thanks for the replies.
GrantF is offline

Old 04-14-2016, 04:37 PM
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You won't be able to get enough potassium from KH2PO4. You'll need to use another fertilizer. Typically, people use K2SO4 for this.

However, the EI method you want to use requires large weekly water changes, 50%. I doubt (though not impossible) your tank will produce sufficient NO3 with the appropriate water changes. Generally, hobbyist can omit KNO3 from the EI dosing method when their tap water has high levels of nitrate. Just some food for thought

If you want to omit KNO3 then dose the amounts below...

Dose 30 ml of the solution three times per week

Add the following amounts to your 900ml container

KH2PO4 6.77 gm (approximately 1 1/4 teaspoons)
K2SO4 56.4 gm (approximately 8 3/4 teaspoons)

Each 30 ml dose will add the following to your tank,

PO4 1.3 ppm
K 7.5 ppm
Zorfox is offline
Old 04-14-2016, 05:11 PM Thread Starter
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Damn, ok. I dosed micros this morning, so I plan to test nitrates tonight to see where they're at.

How did you get to those numbers?
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Old 04-14-2016, 05:19 PM
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Quote:
Originally Posted by GrantF View Post
I dosed micros this morning, so I plan to test nitrates tonight to see where they're at.
You still need to dose micros. Typically EI suggests dosing macros and micros on alternating days.

Here is a post I made about EI. After reading this, hopefully things will make a little more sense to you, The EI Concept explained

Quote:
Originally Posted by GrantF View Post
How did you get to those numbers?
From a Windows based calculator I wrote, Zorfox's Planted Tank Calculator

Here is another that seems accurate that you can check out, Rotala Butterfly | Planted Aquarium Calculators & Information

The one you are using seems to not be accurate. I will try and contact them to see if I can help. For now, the numbers coming from there are wrong.
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Old 04-14-2016, 06:13 PM Thread Starter
Algae Grower

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Posts: 146
Quote:
Originally Posted by Zorfox View Post
You still need to dose micros. Typically EI suggests dosing macros and micros on alternating days.

Here is a post I made about EI. After reading this, hopefully things will make a little more sense to you, The EI Concept explained
Thanks for the reply.

I understand the concept of EI and how it works etc, but the point I was making was that my nitrate levels today should be lower given that I dosed micros this morning rather than macros. Are you implying that plants don't use the nutrients in your tank within 24 hours (i.e. the macros that I dosed yesterday would still be present in the tank tonight)?

Quote:
Originally Posted by Zorfox View Post
From a Windows based calculator I wrote, Zorfox's Planted Tank Calculator

Here is another that seems accurate that you can check out, Rotala Butterfly | Planted Aquarium Calculators & Information

The one you are using seems to not be accurate. I will try and contact them to see if I can help. For now, the numbers coming from there are wrong.
Thanks.

Damn that sucks. I just made a fresh batch of micro's last night. I'll take a look at your calculator later on and see what it gives me.
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Old 04-14-2016, 06:41 PM
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Quote:
Originally Posted by GrantF View Post
Thanks for the reply.

I understand the concept of EI and how it works etc, but the point I was making was that my nitrate levels today should be lower given that I dosed micros this morning rather than macros. Are you implying that plants don't use the nutrients in your tank within 24 hours (i.e. the macros that I dosed yesterday would still be present in the tank tonight)?
If you have to ask that, it doesn't seem like you understand EI. EI dosing, in short, is giving the plants more nutrients than it needs so that plants are limited only by light. You will not only not run out of macros, they will accumulate if you don't do water changes. So to answer your question, if you dose properly you will always have left over nutrient from the last time you dose.
Navyblue is offline
Old 04-14-2016, 07:13 PM Thread Starter
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Quote:
Originally Posted by Navyblue View Post
If you have to ask that, it doesn't seem like you understand EI. EI dosing, in short, is giving the plants more nutrients than it needs so that plants are limited only by light. You will not only not run out of macros, they will accumulate if you don't do water changes. So to answer your question, if you dose properly you will always have left over nutrient from the last time you dose.
Lol touché.

I just took a quick read through Zorfox's link, and I have a two questions.

1) As long as you are above the minimum required nutrient level for individual nutrients, do relative differences between the nutrient levels matter?

2) To determine the amount of a dry fertilizer to add to your stock solution would you do the following:
- Say 120L tank, 900 mL dosing bottle, 30mL doses, and target concentration of nutrient X is 7.5 ppm.

7.5ppm=0.0075 g/L * 120L tank = 0.9g/dose

0.9g/30mL dose = 0.03 g/mL required in the dosing container

0.03g/mL * 900mL dosing container = 27g of dry nutrient X

i.e. add 27g of nutrient X to the container when you're making your stock solution. Is this correct?
GrantF is offline
Old 04-14-2016, 08:07 PM
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Quote:
Originally Posted by GrantF View Post
1) As long as you are above the minimum required nutrient level for individual nutrients, do relative differences between the nutrient levels matter?
Nope. You will see a lot of people say that certain nutrients should be in specific ratios. However, when supplying nutrients in excess this does not apply.

Quote:
Originally Posted by GrantF View Post
2) To determine the amount of a dry fertilizer to add to your stock solution would you do the following:
- Say 120L tank, 900 mL dosing bottle, 30mL doses, and target concentration of nutrient X is 7.5 ppm.

7.5ppm=0.0075 g/L * 120L tank = 0.9g/dose

0.9g/30mL dose = 0.03 g/mL required in the dosing container

0.03g/mL * 900mL dosing container = 27g of dry nutrient X

i.e. add 27g of nutrient X to the container when you're making your stock solution. Is this correct?
That would give you a correct dose provided the fertilizer is 100% nutrient X. However, none of them are. Lets do KNO3 as an example.

Here is the formula we can use.

Dose for 1 liter (mg) = ( Desired Concentration (as ppm) / % of element in fertilizer ) * 100

To see what percentages are in each fertilizer you can use a molar mass calculator. This will tell you the percentages of each element in a substance.

Enter KNO3 into the calculator link above and you will see that KNO3 has 13.8539% Nitrogen.

Since we want NO3 and not N we have to do a conversion since the weight of N and NO3 are different. To get the weight of each you can enter them in the calculator.

N = 14.0067
NO3 = 62.0049

So to get the factor to multiply by we divide, (here is a list of conversion factors, Conversion Tables so this step can be omitted)

62.0049 / 14.0067 = 4.4268

This means to convert N to NO3 we multiply by 4.4268

13.8539 (percent of N in KNO3) * 4.4268 = 61.3284

So KNO3 has an equivalent of 61.3284% NO3

Now we can do our calculation...

mg = (7.5 / 61.3284) * 100
mg = 0.1223 * 100
mg = 12.23

So if we need 12.23mg per liter we need 120 times that for 120 liters.

12.23 * 120 = 1,467.6 mg (or 1.4676 grams)

If you want a solution divide the dose size into the container size and multiply by the dose, i.e.

(900 ml / 30 ml ) * 1,467.6 = mg to add to your container

30 * 1467.6 = 4,4028 mg

So we add 4.4028 grams to our 900ml container and dose 30ml each time to raise NO3 7.5ppm

Note I rounded the number throughout these calculations so the numbers won't match calculators perfectly.
Zorfox is offline
Old 04-14-2016, 11:57 PM Thread Starter
Algae Grower

Join Date: Jan 2015
Posts: 146
Quote:
Originally Posted by Zorfox View Post
Nope. You will see a lot of people say that certain nutrients should be in specific ratios. However, when supplying nutrients in excess this does not apply.

That would give you a correct dose provided the fertilizer is 100% nutrient X. However, none of them are. Lets do KNO3 as an example.

Here is the formula we can use.

Dose for 1 liter (mg) = ( Desired Concentration (as ppm) / % of element in fertilizer ) * 100

To see what percentages are in each fertilizer you can use a molar mass calculator. This will tell you the percentages of each element in a substance.

Enter KNO3 into the calculator link above and you will see that KNO3 has 13.8539% Nitrogen.

Since we want NO3 and not N we have to do a conversion since the weight of N and NO3 are different. To get the weight of each you can enter them in the calculator.

N = 14.0067
NO3 = 62.0049

So to get the factor to multiply by we divide, (here is a list of conversion factors, Conversion Tables so this step can be omitted)

62.0049 / 14.0067 = 4.4268

This means to convert N to NO3 we multiply by 4.4268

13.8539 (percent of N in KNO3) * 4.4268 = 61.3284

So KNO3 has an equivalent of 61.3284% NO3
Can you not just determine the molar mass of NO3 and divide by the molar mass of KNO3? It gives you the same number.

Quote:
Originally Posted by Zorfox View Post
Now we can do our calculation...

mg = (7.5 / 61.3284) * 100
mg = 0.1223 * 100
mg = 12.23

So if we need 12.23mg per liter we need 120 times that for 120 liters.

12.23 * 120 = 1,467.6 mg (or 1.4676 grams)

If you want a solution divide the dose size into the container size and multiply by the dose, i.e.

(900 ml / 30 ml ) * 1,467.6 = mg to add to your container

30 * 1467.6 = 4,4028 mg

So we add 4.4028 grams to our 900ml container and dose 30ml each time to raise NO3 7.5ppm

Note I rounded the number throughout these calculations so the numbers won't match calculators perfectly.
Thanks for the explanation, that makes sense. What concentrations do you recommend for the different nutrients? I know you included ranges in your link, but they're pretty sizeable. Potassium for example is 10-30, so do I just aim for 20?
GrantF is offline
Old 04-15-2016, 12:41 AM
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No. KNO3 just happens to be a coincidence.

Suppose you want the equivalent amount of NO3 from urea.

The molar mass of urea (CH4N2O) is 60.0553. NO3 has a molar mass of 62.0049. So if you do the math you suggest you would end up with a negative number.

Urea is 46.6460% nitrogen.

So to get the NO3 equivalent of urea (note this is an equivalent NOT actual NO3) we multiply 46.6460 * 4.427 = 206.501842

mg = ( 7.5 / 206.501842 ) * 100
mg = 0.03632 * 100
3.632mg per liter

Make sense?

As far as the levels of each nutrient is concerned, yes 20ppm would be a good target for NO3. Those numbers were devised by Tom Barr not me. As long as you maintain the lowest number you should be okay. You simply never want to drop below that number. The high end? Well I would say that is dependant on your tank inhabitants. Plants can certainly tolerate much higher levels. Example, Hoagland solution calls for 210ppm of Nitrogen. That's the equivalent of 930ppm of NO3!
Zorfox is offline
Old 04-15-2016, 02:03 AM Thread Starter
Algae Grower

Join Date: Jan 2015
Posts: 146
Interesting. So does the "molar mass fraction" way of doing it only work when NO3 or whatever compound you're looking at is in the chemical formula to begin with? I'm guessing that the "equivalent" NO3 is based on when the urea dissociates in water?
GrantF is offline
Old 04-15-2016, 02:39 AM
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If the NO3 in your aquarium is from fish food, then you may want to adjust the P and micros, also.
Fish food is fairly high in N, P and most micros.
Fish food is low in K, Fe, Ca and Mg.

If your water has a GH of at least 3 German degrees of hardness, then you probably do not have to dose Ca or Mg.

In tanks where the fish food is the main source of N, P and most micros, dose K (K2SO4) and chelated iron.

If you need to dose just a little bit of KNO3, then also dose just a little bit of KH2PO4 and just a little bit of micros. Keep these ratios similar to the EI dose, just a lot less.

Example:
The full EI recipe for a 32 gallon tank is:
1/4 Tsp-KN03 3x a week
1/16 Tsp-KH2P04 3x aweek
1/2 Tsp-GH booster once a week
1/16Tsp-Trace 3x a week
Optional
1-2ml-Fe/Iron 3x a week
(Alternate way to figure iron: 25% of the amount of the micros, using CSM+B for traces and (dry) chelated iron)

But if the fish food is supplying enough NO3 that you want to cut the KNO3 by 50%, then the recipe would look like this:

1/8 tsp KNO3 (50% of the above recipe)
1/32 tsp KH2PO4 (50% of the above recipe)
1/8 tsp K2SO4 (It is easy to substitute K2SO4- however much KNO3 you omit, dose that much K2SO4. The chemical formula is not exact, but as noted above, it is not that critical)
(GH booster is optional- 1/2 tsp is not a problem for most fish, but if the GH is already high enough no need to dose more.)
1/32 tsp trace (50% of the above recipe)
1/64 tsp chelated iron (amount may vary- there are several forms of chelation, and the iron content varies a bit)
Diana is offline
Old 04-15-2016, 03:18 AM
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I have been checking my nitrates and phosphate with test kits and find its the best way to maintain consistent macro levels. Having a test kit will also help you to find the best fertilization ratios for your tank.

Interestingly when I use citric acid or vinegar as a buffering agent the nitrate levels plummet. At high nitrate+citrate levels a bacterial bloom will be present. I believe the weak organic acids provide a sugar source for bacteria that also end up consuming nitrates. Its is very likely that when carbon levels build up in aged tanks that nitrate may also end up getting consumed by bacteria.
rezco is offline
Old 04-15-2016, 05:20 AM
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This is off topic, but you do not want to use organic compound as buffer in aquarium. They will be decomposed and consumed by bacteria. Their effect is short lived at best and you will have other problem to deal with. Dosing vinegar and citric acid is that is what reef folks do to lower nitrate and phosphate. And most organics will of course decompose into inorganics in time. C will end up as CO2 and escape into the atmosphere, N and P will turn into nitrate and phosphate and remain in water.

Another main point EI dosing is to provide plants enough nutrient without water testing. We can test for some things, but not for most things that plant needs. Even those that we can test, the accuracy of the hobbyist level test kits are very questionable. I have 2 nitrate kits, Salifert and Seachem. Both are supposed to be the best hobbyist grade kits one can find, one says I have 30ppm another says I have 75 ppm. So which is it? IMO they only sorta hint when you would need a water change for fishes, or when you really bottom out on a specific nutrient (not gonna happen with EI), but that's about it.

Not to mention plant consumption will vary on various interconnecting factors, with what we have it is hard enough to hit a stationery target, let alone a moving one. If you have a good regime like EI, honestly the benefit provided by a hobbyist level test kit are rather marginal and the money is better spent else where.

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