Is My EI Dosing Accurate?

[tjbuege]

Hi all,

I know, this stuff is laid out to be easy, no need to calculate, etc... That's all good, and I'm using it, but I'm never one to let that sort of thing be, so I just had to figure the math behind it all. I always want to know the how and why of things, and to verify what others say. This post is more for a sanity check, and to make sure I'm not way off base.

First some assumptions (and I apologize for the MATH, but I just HAVE to know... ): KNO3 weighs 5.6 grams per tsp and contains 68.328% NO3 and 38.672% K, and KH2PO4 weighs 4.8 grams per tsp and contains 28.731% K and 69.788% PO4. I arrived at these numbers from various sources, including Chuck's Planted Aquarium Calculator, and sites such as http://www.convertunits.com/molarmass/KNO3. I'm also assuming each aquarium contains 85% of it's capacity in water, due to substrate, etc. So a 29 gal tank has 93.3 liters and a 20 gal tank has 64.4 liters.

I prefer to dose daily (easier for me to remember) using a liquid solution. I mix up my solution with 450ml of water. Into the water I mix 5 tsp (28 grams) of KNO3 and 1/2 tsp (2.4 grams) of KH2PO4. The resulting solution contains 35,745 ppm of NO3, 22,540 ppm of K and 3,486 ppm of PO4. With me so far?

Now, I chose these amounts so that I could dose both my 20 gal and my 29 gal using the same mixture, and simply dose a diff amount into each tank. The 20 gal receives 6 ml of this solution daily, and the 29 gal receives 9 ml daily. And I do 50% water change weekly.

I figure I am dosing the following weekly, and this is the part I want confirmed:

29 gal: 9 ml solution daily provides 24.1 ppm NO3, 15.2 ppm K and 2.4 PPM PO4 weekly.
20 gal: 6 ml solution daily provides 18.9 ppm NO3, 11.9 ppm K and 1.2 PPM PO4 weekly.

Are my calcs accurate? Is this an appropriate amount to dose (meaning, is it way too much or to little)?

(BTW, I also dose micros, but I'm leaving that out of this conversation for the moment).

Once I'm comfortable that this is correct, I'll file away the calculations and forget about them, and simply remember how much of what to add and dose.

Any thoughts?

Thanks,

Tim

 

[Biollante]

I Will Double Check


Hi,


I am confused.


It appears to me in a convoluted sort of way that you are dosing at best
5-ppm NO[SUB]3[/SUB] per week
.12-ppm PO[SUB]4[/SUB] per week
4.2-ppm K[SUP]++[/SUP] per week

Just as a matter of approximation, you are making a solution you intend to dose about 160 liters with 15-ml per day, so your 450-ml solution (not correct but we’ll go with it), that is 30 days’ worth of dosing.

• Dose one teaspoon of KNO3 and a half-teaspoon of KH2PO4 seem reasonable?
  

• Put another way, would dry dosing 0.19 gram of KNO3 and 0.08 gram of KH2PO4 seem reasonable?

Biollante

 

[tjbuege]

I am confused.

Yeah, I was afraid I was rattling a bit. I was trying to explain where I come up with the numbers. I'll put it more simply:

I create my solution by mixing 5 tsp KNO3 and 1/2 tsp KH2PO4 with 450ml of water.

Using this solution, I dose 9ml DAILY to my 29 gal tank and 6 ml DAILY to my 20 gal tank.

I dose both tanks 7 days a week, and change the water 50% once a week.

By my calculations I am dosing a total of:

24.1 ppm NO3, 15.2 ppm K and 2.4 PPM PO4 weekly in the 29 gal
18.9 ppm NO3, 11.9 ppm K and 1.2 PPM PO4 weekly in the 20 gal

Does this help explain what I'm dosing, or did I just repeat myself?

Tim

 

[Biollante]

I Hate When Real Life Gets In The Way!


Hi,

Sorry I didn’t get the whole thing posted, real life is rearing it’s ugly head.

Sorry I guess I missed the 5 teaspoons that is better. I think I see where you went wrong.



I will post later with my suggestion.:gw


Biollante

 

[tjbuege]

Ok, sounds good. I was going to try and reply with my formulas, but not off the top of my head. I have this all worked out in a spreadsheet at home, and I'm eager to know where it's wrong.

Thanks!

Tim

 

[tjbuege]

Couldn't Leave It Be!

Fired up Excel and reworked this. I'm getting the same results I did before.

This is my understanding of the chemical breakdown of KNO3 and KH2PO4:

(see http://www.convertunits.com/molarmass/KNO3 and http://www.convertunits.com/molarmass/KH2PO4)

	Composition

		KNO3	KH2PO4
		-------	-------	
K		38.7%	28.7%
NO3		61.3%	
PO4			69.8%
		
	Weight (per tsp)

		KNO3	KH2PO4
		-------	-------	
Total		5.6 g	4.8 g
K		2.17 g	1.38 g
NO3		3.43 g	
PO4			3.35 g
		
	Weight (in solution)

		KNO3	KH2PO4
		-------	-------	
Quantity	5.0 tsp	0.5 tsp
K		10.83 g	0.69 g
NO3		17.17 g	
PO4			1.67 g

Amount of water in solution = 450 ml
Weight of water in solution = 450 g

Here's the breakdown of the solution, in weight, % and ppm:

Composition (of solution)	480.4 g	total wt.

H2O		450 g	93.7%	936,789 ppm
K		11.5 g	2.4%	23,977 ppm
NO3		17.2 g	3.6%	35,748 ppm
PO4		1.7 g	0.3%	3,487 ppm

And the breakdown of 1 ml of solution:

H2O		0.937 ml
K		0.0240 g
NO3		0.0357 g
PO4		0.0035 g

A 29 gal aqaurium holds 109.8 liters or 109,777 ml of water
Dose size is 9 ml.

	Dose		Ratio/Tank	Daily		Weekly
K	0.2158 g	0.00020%	 2.0 ppm	13.8 ppm
NO3	0.3217 g	0.00029%	 2.9 ppm 	20.5 ppm
PO4	0.0314 g	0.00003%	 0.3 ppm 	2.0 ppm

A 20 gal aqaurium holds 75.7 liters or 75,708 ml of water.
Dose size is 6 ml.

	Dose		Ratio/Tank	Daily		Weekly
K	0.1439 g	0.00019%	 1.9 ppm	13.3 ppm
NO3	0.2145 g	0.00028%	 2.8 ppm 	19.8 ppm
PO4	0.0209 g	0.00003%	 0.3 ppm 	1.9 ppm

And that's close to what I had in the first place.

If I went wrong some where, please enlighten me!

Tim

 

[Biollante]

Well Okay... The Kitchen Sink as Well


Hi Jim,

Once again my apologies, I was delinquent in my due diligence. If my apology for my error isn't good enough, so be it. I made a mistake it is not my first it won't be my last, I am sure.


It appears your results are within the bounds of reason.


Also, let me say I am not interested in proxy arguments. If another site says do it this way, and I say another, it is your choice.

Two pieces of nit to pick,[SUP]1[/SUP]

• First, the ridiculous, phony[SUP]2[/SUP] precision of numbers, I know you have spreadsheets and calculators and computers, put really, even with reagent grade chemicals and analytical scales, no way we get into the part per billion or trillion accuracy.
• Second, there is already a built in error in the way we calculate our parts per whatever of solutions.[SUP]3[/SUP] When calculating the solution, in your case 450-ml, which is nice since that is 30 days of dosing, it is best to begin with less than 450-ml[SUP]4[/SUP] of distilled water, say 400-ml maybe a bit less. Add the salts, dissolve thoroughly, and add enough distilled water to dilute the to 450-ml.

Anyway have fun!


Biollante
[SUP]1[/SUP]Without nitpickers we would not have the wonderful cotton products we enjoy!
[SUP]2[/SUP]As in kidding yourself that any such precision can cause anything but real world confusion.
[SUP]3[/SUP]As a practical matter we accept that the density of the components of our solute is equal to the density of water on a standard day.
[SUP]4[/SUP]For better accuracy weighing the water, correcting for deviation from standard day, by definition each milliliter of water equals one gram.

 

[tjbuege]

Hi Jim,

Once again my apologies, I was delinquent in my due diligence. If my apology for my error isn't good enough, so be it. I made a mistake it is not my first it won't be my last, I am sure.


It appears your results are within the bounds of reason.


Also, let me say I am not interested in proxy arguments. If another site says do it this way, and I say another, it is your choice.

Oh, no no no.... I'm not judging or criticizing anything you have said or any mistakes you may have made... BTW... What mistake? Not sure you ever got around to saying, unless you are referring to missing the 5tsp of KNO3. Anyhow, I make mistakes all the time. No apologies required.

Two pieces of nit to pick,[SUP]1[/SUP]

• First, the ridiculous, phony[SUP]2[/SUP] precision of numbers, I know you have spreadsheets and calculators and computers, put really, even with reagent grade chemicals and analytical scales, no way we get into the part per billion or trillion accuracy.

Hahaha...... ! Touche! Yeah, yeah, I know. But hey, the spreadsheet has huge precision.... I was already truncating and rounding before posting my numbers!!

But remember, my goal in originally asking about this is to understand the math. But anyhow, I wasn't trying to be rediculously precise, that's just how the numbers were pasted into my messafe. Your point is taken and received.

• Second, there is already a built in error in the way we calculate our parts per whatever of solutions.[SUP]3[/SUP] When calculating the solution, in your case 450-ml, which is nice since that is 30 days of dosing, it is best to begin with less than 450-ml[SUP]4[/SUP] of distilled water, say 400-ml maybe a bit less. Add the salts, dissolve thoroughly, and add enough distilled water to dilute the to 450-ml.

Ok, what's the purpose of starting with only 400ml, then topping off to 450ml? This is the first time I've seen this suggestion. I'm honestly curious what the benefits are.

Anyway have fun!

Yes, definitely having fun with this. If I were not having fun, I'd not be asking.

Biollante
[SUP]1[/SUP]Without nitpickers we would not have the wonderful cotton products we enjoy!
[SUP]2[/SUP]As in kidding yourself that any such precision can cause anything but real world confusion.
[SUP]3[/SUP]As a practical matter we accept that the density of the components of our solute is equal to the density of water on a standard day.
[SUP]4[/SUP]For better accuracy weighing the water, correcting for deviation from standard day, by definition each milliliter of water equals one gram.

And your footnotes are precisely correct. I have no allusions that any high precision adds anything to the plants or tank. It's just a part of my quest for understanding. Once I understand, I will go back to simple, lower precision that is "good enough". After all, how much is a tsp? How can I know I have EXACTLY the same amount of dry ferts in each one?

Good point about density of water. I'm using the assumption that 1g = 1ml, as you stated. A good shortcut to take.

Thank you very much for your feedback. I'm much more confident now that I'm not off base here.

Tim (not Jim... )

 

[Wet]

Expanding the same thoughts as my favorite Plant Monster, this isn't totally accurate:

Amount of water in solution = 450 ml
Weight of water in solution = 450 g

Here's the breakdown of the solution, in weight, % and ppm:

Composition (of solution)	480.4 g	total wt.

H2O		450 g	93.7%	936,789 ppm
K		11.5 g	2.4%	23,977 ppm
NO3		17.2 g	3.6%	35,748 ppm
PO4		1.7 g	0.3%	3,487 ppm

Of course, that's not really 450mL of water (it's 450mL - the volume of the other stuff), and therefore not 450mg either. But the big point is it doesn't matter so much. I actually think calculators should be as accurate as they can while humans should round as humans are prone to do The calc is just a tool and we should then exert our best judgement.

By this same thought, you know if you do two bottle caps into the 29 and one into the 20 (~10mL and ~5mL respectively instead of 9mL and 6mL) you've got an easy dosing routine well within the margins of error of Ei.

---

edit: late to the party and already addressed

 

[tjbuege]

Well.... not to belabor the point..... actually.... the way I mix the concoction, I believe it really is 480.4 grams in weight total (assuming 1ml = 1g of H2O of course): Start with 450ml water, add 30.4g of dry ferts. Right?

But I think we all understand the unnecessity (is that a word?) of great precision and detail.

I have those nice 450ml bottles with built in measuring cups (with HIGHLY inaccurate graduation marks on them, I might add). I know at which point is 6ml and 9ml. Can't get much easier.

Thanks for the comments!

Tim

 

[Biollante]

6.8% Less


Hi Tim,


Sorry once again, we have a plethora of Jim’s; when in doubt just yell “Jim” and someone will answer.



The difference in the mixing the solution is about 6.8%.



In your example if you mix 30.4 grams of salts into 450-ml (grams) of water you, end up with 480.4 grams of solute. Therefore, your solution is now 6.8% more dilute than you figured.

Now if this formula comes from someone else, it may have already accounted for. It is just that 450-ml (grams) is such a nice fit for a 30 day supply.


I tend to make my solutions in 28-day batches, since I do a lot of auto-dosing and weekly water changes, one of the advantages of making your own solution is making them work for your situation.


Biollante

 

[Wet]

Biollante's last post put another way:

Say I have a container that holds 450mL. I fill it to the brim with water. I then add 6 teaspoons (30 cm^3, or 30mL volume) of some other stuff into that container. What happens to the container? (It'll overflow.)

Most calcs and your science lab will do this another way. Take the 450mL container. Add some water, say, 3/4 full. Add the 6 teaspoons stuff and dissolve it. Fill the rest with water. Now it is a 450mL solution. (But not 450mL water.) This is why calculations avoid mass for such calculations and instead work with the volume of the solution and dose. The big assumption then is everything is homogenous -- completely dissolved and the same concentration throughout the container. This is almost always a safe assumption with the ferts we mess with.

But I suppose another answer to "Is my EI dosing accurate?" is "it's certainly accurate enough!", as you know

 

[tjbuege]

Yep, I'm using 480.4 g in my formulas. For example, to calculate NO3 ppm in the solution, my formula is:

NO3 ppm = weight of KNO3 in solution (28g) * % of NO3 in KNO3 (61.328%) / (weight of water (450g) + weight of ferts (30.4g)) * 1,000,000

In numeric form:

28g * 61.328% / (450 + 30.4) * 1,000,000 = 35,745 ppm NO3 in the solution.

When I dose 9ml of this into a 29 gal tank, I've dosed 2.9 ppm of NO3. Do that 7 days a week, and I've dosed 20.5 ppm NO3.

Similar formulas for K and PO4.

BTW, my solution bottles are graduated to 450ml, but they probably hold much closer to 500ml, if not more. Got them when I bought my ferts online: http://www.aquariumfertilizer.com/i...nEdit=10&Returnitemname=&ReturnShowItemStart=

 

[tjbuege]

Just so you all understand me a bit better, I'm a problem solver. I'm driven by the prospect of figuring out a good mystery. I sometimes LOOK for things to solve (is that like looking for trouble? ). So when I keep responding back with more questions, and keep questioning your responses, I'm not saying I disagree (if I do, I'll say so). I'm usually asking for more clarification. I'm also realistic, and know that when Tom says 10-30ppm is the range we're shooting for, I don't have to measure to get exactly 20.535729 ppm. Anyhow, this stuff IS fun for me, as Biollante suggested. Call me crazy, but it's just plain fun!

I have nothing but high respect for everyone I can think of on this forum. That's why I became a lifetime charter member... not because I have any level of expertise to share, but because I consider the information here invaluable. It's worth every penny.

Tim

 

[tjbuege]

Yes, My Original Question Has Been Answered!

But I suppose another answer to "Is my EI dosing accurate?" is "it's certainly accurate enough!", as you know

Absolutely correct. I just wanted to make sure I had my decimal places in the right spot, so to speak!

(and to verify / clarify the calculations)

Tim

 

[Wet]

Hey Tim. That's clever: I missed that by your ignoring volume in these calculation you actually do take into account the volume of the compounds added to the water. (Because the mass of water + that stuff becomes a proxy for volume.)

 

[Biollante]

Twist It Anyway You Like, >450-ml Is <15-ml X 30


Hi Tim,


I am belaboring the point, you can call yourself a problem solver, lecture me about the advantages of spreadsheets, you can twist words all you want, but by volume or mass, what-have-you if you stuff anything into 450-milliliters of anything you will have more than 450-milliliters. It doesn’t matter how much extra room there is, it is still more than 450-milliliters.


Remember I am the one that said not all this “accuracy” was necessary. Your stated goal was to dispense 15-ml each day, you wanted all this “accuracy,”, unless you increase the dosing by whatever percentage over the 450-milliliters you are, your dosing is light.:gw


I’ll even ignore mixing volume and mass, I will overlook the difference between “accuracy” and “precision." (How magnanimous of me!)


There is no problem when responding with a question, as long as the intended question clarifies rather than obfuscate, or is simply a mechanism to avoid acknowledging error.


Biollante

 

[tjbuege]

Biollante, I think you missed my post above. I'll repeat it here again:

Yep, I'm using 480.4 g in my formulas. For example, to calculate NO3 ppm in the solution, my formula is:

NO3 ppm = weight of KNO3 in solution (28g) * % of NO3 in KNO3 (61.328%) / (weight of water (450g) + weight of ferts (30.4g)) * 1,000,000

In numeric form:

28g * 61.328% / (450 + 30.4) * 1,000,000 = 35,745 ppm NO3 in the solution.

When I dose 9ml of this into a 29 gal tank, I've dosed 2.9 ppm of NO3. Do that 7 days a week, and I've dosed 20.5 ppm NO3.

Similar formulas for K and PO4.

So you see, I AM basing my calculations on 450 ml PLUS the dry ferts. 480.4 g to be exact.

And the very first thing I said in my first post was:

I know, this stuff is laid out to be easy, no need to calculate, etc... That's all good, and I'm using it, but I'm never one to let that sort of thing be, so I just had to figure the math behind it all. I always want to know the how and why of things, and to verify what others say. This post is more for a sanity check, and to make sure I'm not way off base.

All ok now?

 

[Biollante]

Be Happy


Hi Tim,

Whatever, if you are happy, who cares.:gw

I will stick to honest questions.

Biollante