Question About PPM

lucky123April 14, 2014

I found the answer. There is 2.88 ppm P added for every 1 oz of phosphoric acid per 1000 gallons of water

I asked a question about how much P would be in a gallon of water + 2 oz phosphoric acid. Then take 1/8 tsp of that concentrate and add to one quart. How many ppm P in the quart but the answer or at least the necessary components I posted above.
Thanks I found the answer

This post was edited by lucky123 on Mon, Apr 14, 14 at 23:49

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PupillaCharites(FL 9a)

Caution, you are dealing with fluid ounces, not avoirdupois ounces (the normal ounce for weights).

I assume you have 85% phosphoric acid since it does give 150 ppm P2O5 at the dilution you mentioned. However you are then diluting the 100:1 concentrate into water.

1/8 tsp in a quart is 1/2 tsp in a gallon. So, your irrigation water has about 0.5/768 x 15,000, or about 9.8 ppm of P2O5, or 4.26 ppm elemental phosphorus (P) the way most people measure nutrients by the element, not the oxide. You don't give the dilution ratio of your fertilizer, so let's assume your fertilizer added to the same quart of water contains 35 ppm of elemental phosphorus, which ought not be off by more than 50%.either way. (35+4.26)/35 = 1.122 would be the number your multiply the "P" of the NPK to put it in the terms you asked. So if the "P" is 2, the new P will be 2 x 1.122 = 2.244, which sounds like it is no problem, in the ballpark of 10% increase in phosphorus.

    Bookmark   April 15, 2014 at 12:52AM
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I converted everything to fl oz
The formula is
1oz phosphoric acid in 133600 oz = 2.88 ppm

2.88 x 133600 = 384768 (the value of 1 oz of phosphoric)

My concentrate is 2.88 x 2 x 1000 = 5760 ppm in 1 gallon water

.02 oz concentrate in 32 oz (1 qt water) = ?

1/8 tsp is .02 oz of 5760 concentrate

5760 x .02 = 115.2 / 32 oz = 3.6

I am not good at math. I am close to what you got so what is a few decimal points amongst friends?
Thank You So Much For Answering This!

    Bookmark   April 15, 2014 at 1:32AM
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Hi Lucky
When you make stock/concentrated solutions you shouldnt add the chemical to the total water volume as it wont be accurate. Put less than the total water in, add the chemical and let it dissolve, then top up the water to the correct amount. The water used for stocks should be as pure as possible.

    Bookmark   April 15, 2014 at 8:24AM
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PupillaCharites(FL 9a)

It won't hurt to wish you good luck, Lucky. I was watching a movie and answered your question during a break without refreshing so my answer references information that you deleted in the original post, which was geared towards the original questions you asked about relating how the the Phosphorus Pentoxide (P2O5) rating of the the NPK of your fertilizer, would change based on the amount of phosphoric acid you were adding. In the original information you didn't provide the dilution factor of your fertilizer but you did mention that 2 fluid ounces of your phosphoric acid in 100 gallons yielded a solution with "150" which you said was the P2O5 you wanted to relate to the NPK.

Check my math if you like, but a standard phosphoric acid many purchase is 85%, which just happens to give 150 ppm of P2O5 when diluted 2 ounces into 100 gallons so although you never said the concentration of the acid, of key importance, it was too much a coincidence that the number was right for the standard phosphoric concentrated acid (85%). It was strange to me that you had the number for ppm P2O5, rather than P elemental, but I wasn't about to second guess that part.

The problem now, is that you state 2.88 ppm of P (elemental phosphorus) is the result of 1 fluid ounce of the phosphoric acid in 1000 gallions, information you 'found'.

85% acid does not give 2.88 ppm at that dilution, however another common concentrate which is 75% does (well, it gives closer to 2.9 ppm although 2.88 is often quoted.

So, the first thing to do is just confirm the concentration of whatever acid you actually have, since the new info is inconsistent, which gives me the idea that you are getting the info from at least one other source that is not written on your bottle and applies to a different concentration.

That said, among friend sure, absolutely, the bottom line is still the same, whether we are talking about 3 ppm or 5 ppm of phosphorus BFD - if the solution of fertilizer gives 30-50ppm of P, that's around 10% extra which you need a good hand to measure accurately anyway when using teaspoons.

Final observation is, good you are no longer concerned about the NPK written on the fertilizer bottle more than actually the nutrient ppm in solution, you've probablly learned a lot and quickly, and I think your math is not convention but basically fine.

It is very good form to dilute to total volume, when making the stock solution, but that happens to be negligible for this due to the minor amount of acid (a dilution factor well within 1% whether you do that or not). Let me suggest that you and I have possible both done it right and the difference between your 3.6 ppm P and my 4.2 ppm P is due to the concentration of acid not being consistent:

4.2 ppm P x 75%/85% = 3.7 ppm P

and that no matter how many small differences there are, in the big picture you still see your ballpark addition of phosphorus is 10% more than a typical fertilizer, and you now can calculate exactly the increase if you want to by considering the dilution ratio of the fert you never posted. But seriously, you probably think it is unecessary now that you see the magnitude is relatively insignificant if you aren'ty doing a research paper on it! But do check you phosphoric concentration to be sure you have what you think ;-)

    Bookmark   April 15, 2014 at 4:11PM
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Dilution Ratio of the Fertilizer!

That is the answer to the Next Question. The NKP adjustment, isn't it!

Thank You, now I know how to do the Fertilizer, Yes?

I have read the information you posted, copied it to a file and learned many things.
I just read different ppm ratings on different web sites for greenhouses and used the figures posted. I didn't realize it was different concentrations.
Your post is really intelligible to a math challenged person such as myself.
Diluting concentrations has always been tricky for me.
I am not hydroponics. I am African Violet hobbyist with very alkaline water. But I thought someone here would know the solution to the solution, so to speak :)
Thank you very very much.

This post was edited by lucky123 on Tue, Apr 15, 14 at 19:16

    Bookmark   April 15, 2014 at 6:30PM
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PupillaCharites(FL 9a)

Glad it helped, I know going through someone else's logic can be like going through a 1040 instruction book for the first time ;-(

I think you've got it ... the NPK macrronutrients are listed in the fertilizer numbers by weight. So a 6-4-9 NPK fertilizer is by weight, by definition:

6% elemental nitrogen (N)
4% phosphorus pentoxide (P2O5)
9% potassium oxide (K20)

This is confusing and don't even ask why, all we want usually is the elemental ppms which we get from the elemental percents. Nitrogen stays the same, but approx., P=P x 0.426, and K=K20 x 0.83. So if companies didn't continue to market inflated numbers, the true elemental percents for an NPK 6-4-9 fertilizer would be 6-1.7-7.5.

Now that you can get the elemental percents of each nute of the fertilizer reduce it by the dilution factor (weight/weight) and to convert percent to ppm multiply by 10,000.

The different ppms of each plant recipe's ingredients, though, depends on each plant's favorite nutrient punch and involves a little art to select the right mix.

    Bookmark   April 16, 2014 at 3:35AM
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Here is how I understand what you wrote.
I have an 8 oz bottle of AV fertilizer 7 -7 -7, mix 7-10 drops(1/8 tsp) in quart of water and use every watering.

Question: Is that 7* 7% of the bottle weight, meaning 7% of 8 oz N, 7% of 8 oz P ? 7% of 8 oz K?

Then N = .56 oz P =.24 oz K = .47 oz
Is that right?
Dilution 1/8 tsp to 1 Qt
1/8 tsp = .02 oz
1 Qt = 32 oz
.56N x.02 = .0112/32 = .00035% x 10,000 = 3.5ppm N
.24P x.02 = .0048/32 = .00015% x 10,000 = 1.5ppm P
.47K x.02 = .0094/32 = .00029% x 10,000 = 2.9ppm K

Now if this is correct.
I am adding 4.2 ppm P for PH adjustment so the P would be 5.7. Is the water adjustment P all usable so I add the whole amount back into the .24 of the bottle?

From what I can tell, it would be 7 11 7

Does that seem like a good ratio or is the P too high based on ppm P

(Please correct my math if need be, just don't laugh. I am not good at this)

This post was edited by lucky123 on Wed, Apr 16, 14 at 23:28

    Bookmark   April 16, 2014 at 9:17PM
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PupillaCharites(FL 9a)

A gram scale is the only way to go here, these teaspoons are pretty useless except for a general idea since they cannot be accurately measured, hydro is a precise science when you look for apples to apples comparisons and reproducibility. Here's a simpler method, ignoring the fact we are dealing with fluid ounces which will underestimate since you are not weighing what you put in. A fluid ounce is not an avoirdupois ounce and can weigh between 30 and 40 grams, and the NPK %'s are by weight.

A 7% P2O5 fertilizer is a 3% P fertilizer. Your dilution factor is 1600, so the ppm is 3/1600 x 10,000 = 18.75 ppm if you forget to adjust for the dense fertilizer and that a quart is less than a liter.

If you used a scale you will find it is actually 22-25 ppm P but that's the general idea. So the 4 ppm of the acid adjustment is of no consequence and may be considered nutritional phosphorus from the acid the plant can use since we are using a rather dilute irrigation water with around 50 ppm nitrogen and 40 ppm potassium. (just eyeballing it) As an aside, that is about half strength of commercial growers

UF African Violets

    Bookmark   April 17, 2014 at 12:58AM
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Thank You
Metric is easier. My numbers are too far off. I will go over it carefully, using a gram scale and liters to see if I can get your numbers or at least a bit closer.
Thanks Again.

    Bookmark   April 17, 2014 at 1:18AM
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PupillaCharites(FL 9a)


The beauty of the metric system is nutrient ppm is directly related to mass in grams and liters of water. ppm are the same as milligrams per liter (mg/L).

It is so ironic the US is burdened with these sorts of obsolete calculations when you consider that it was the first country in the world to try to adopt the decimalization of currency, weights and measures as being "American".

Unfortunately, only the decimalization of the dollar stuck, making the US the first country in the world with a completely decimalized currency. Although France is usually considered the cradle of the metric system, when they established the metric system it was strongly influenced by Thomas Jefferson, Benjamin Franklin, Alexander Hamilton and other American founding fathers who wished to shed colonial and imperial systems.

The American Revolution established decimalization and metrication as the rejection of obsolete royal systems which galvanized the French politically to continue the process largely begin by the American revolution in the French revolution 5-10 years later.

More than two centuries later on the planet, only the United States and the African nation of Liberia are still perceived to use imperial-type systems. In 1999 Thailand converted, and in 2011 Myanmar began its conversion citing difficulties with changing the customs of street vendors as the principal impediment to modernization. Liberia is not perceived as metric for the moment, but considering it is severely non-industrialized, the only reason it is mentioned as being as non-metric, considering the weak government thinks the country is metric, is because the coffee industry is having difficulty changing from pounds, all 0.7 million pounds of coffee they produce and export, much to the US. The US consumes 3,000 million pounds annually, almost a quarter (the official US unit for 25 pounds) of which I claim, mostly when I post here :-)

This post was edited by PupillaCharites on Thu, Apr 17, 14 at 12:02

    Bookmark   April 17, 2014 at 11:51AM
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The Custom of the Natives
The only people who use weights and measures daily in the US are Cooks.
All the recipes are qt, c, tbsp. I have not used metric/percentages since high school but I use divisions of tsp/tbsp, cups and ounces day in day out . I can eyeball 10 drops as approx. 1/8 tsp +/- 2 drops (vanilla).
Since everything is premeasured and prepackaged, local natives don't use any system and the cooks resist metric.
Thank you so much for showing me the way to do this correctly. Metric is easier (except for cooking) and weights are not percentages
I saved all of this for future reference.
Thank You So Very Much

This post was edited by lucky123 on Thu, Apr 17, 14 at 15:03

    Bookmark   April 17, 2014 at 12:49PM
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PupillaCharites(FL 9a)

"weights are not percentages"

Just checking up on what you meant. You meant:

"fluid ounces are not weights"

(or "fl. oz. are not mass" for nerds)? I'm sure you have it all figured out by now, but just making sure.

Let's make this post the more important one to save for practical reasons of your 7-7-7, if you convert fluid ounces of water to avoirdupois (weight, always 28.3495 g) ounces, there are 1.04318 ounces (weight) in one fluid ounce of distilled water which weighs 29.5735 grams.

However, being a denser material, one fluid ounce a bottle of Miracle Gro 7-7-7 African Violet fertilizer concentrate weighs 35.5 grams. Alternately, one standard teaspoon of it weighs 5.915 g.

The dosage of 7-10 drops in a quart, say 8.5 drops, is 0.425 mL, or 0.51 grams the way I measure drops, although my 8.5 drops from a standard dropper only gives 0.0719 of a teaspoon, not 0.125 of a teaspoon (1/8 tsp) like yours does. For my drops, the ppm of nitrogen in a quart (0.95 L) for Miracle Gro 7-7-7 Nitrogen is 0.07*510 mg/0.95L, or 38 mg/L = 38 ppm. As you study this, you can write off the difference of 38 ppm N with my dropper, to actually 66 ppm Nitrogen if in fact you are putting 1/8 teaspoon of fertilizer in there. This is why using drops and teaspoons is hairy and grams are the way to go. 38 ppm vs. 66 ppm ... which is it? Ask the dropper? Reminds me of an old joke on why certain people think (hold index fingers 6 inches apart) is more inches... The eye is pretty good to reproduce the quantity, but if the calibration is off, manufacturers, machos, and cheating businessmen can use the confusion to abuse, exaggerate and lie, which assists them in the bottom line of their endeavors...

BTW, the US was primed to switch to the metric system in 1927 and would have and this would all be a big joke today. It was not a revolt among the population at that time that prevented the switch. It was industrial lobbyists for big business in part saying it would cost them too much, and secretly of course, not wanting the public to have transparency in measurement since universal transparency in measurements allows you to easily swap one product for another. This is one big reason we see "trade secret", "proprietary", "art", inflated, misrepresented, abusively truncated, and other deceitful practices on fertilizers.

It is so interesting that the 7-7-7 are percents by weight you are being sold, but, no where on the bottle will you find the weight you are buying. If an alien came to Earth to understand our customs, they would go away scratching their butts if that were their custom to express being perplexed. On the bright side of things, the bottle does have a good conversion into "onzas fluidas", which nobody on the planet has ever used except at gunpoint.

This post was edited by PupillaCharites on Thu, Apr 17, 14 at 15:45

    Bookmark   April 17, 2014 at 3:03PM
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So I would weigh a quantity of the fluid and divide it into grams. Then use a cc syringe to measure out 1cc or 1 ml = 1 gram of that liquid adjusted for the density factor.
Would that work or would it require more sophisticated equipment?
That would be much easier than trying to convert ounces to tsp to ounces certainly.

This post was edited by lucky123 on Thu, Apr 17, 14 at 17:55

    Bookmark   April 17, 2014 at 5:26PM
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PupillaCharites(FL 9a)

You don't need to do anything really except ignore the fluid ounces and just use the scale.

Absolutely nothing besides a $10 gram scale with a resolution of 0.01 grams preferred is necessary for such tiny weights of drops.

In this case you normally would just weigh the 7-10 drops you are using (I would weigh 70-100 drops and divide by 10 since it would give the average of 10 doses.

Also because weighing small amounts sometimes is not accurate on some scales, rather than make a quart, it might be easier to make a gallon since it will require 4 times as much fertilizer and cut down on the weighing uncertainty. Nothing's perfect...

Make believe the liquid is a powder, which doesn't form "drops" or even teaspoons - once you're satisfied you know how much the dose you've always used weighs, use the gram scale whenever you want to quantify your concentrations instead of estimating them, since it is the weight you got in grams to which the 7-7-7 applies.

Most customers using the product, don't need to know more than to add a pinch or smidgen or drop. But that's as long as its +/- 25% and they are not mixing other fertilizers or nutes (like wondering how much 4 ppm P from phosphoric acid changes the phosphorus content of the fertilizer) it really won't matter if they are anything near - the plants are robust.

This post was edited by PupillaCharites on Thu, Apr 17, 14 at 19:36

    Bookmark   April 17, 2014 at 6:36PM
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I just found a .01 gram scale I forgot I had.
And I have a gram scale above 2 grams
So, now I can do as you say and get some proper dilutions.
It is not so critical on the fertilizer but mixing that phosphoric acid is critical to me as I think too much could be a bit hazardous.
I am still copying and pasting your posts in case I get lost again and have to review. Don't mix this stuff very often so better to have some references.

    Bookmark   April 17, 2014 at 7:27PM
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PupillaCharites(FL 9a)

Good luck with it. It's always a good idea to handle concentrated acids with respect.

Don't worry about the amount of acid going ito the solution to pH adjust your water being hazardous to the plants after you are done safely handlng it. If you're adjusting the pH with the acid, as long as the pH is in the good range, nearly all the acid you add has been neutralized and itself converted into some of the same salts in the concentrated 7-7-7 has in much greater concentrations.

For example, the little 8 fluid ounce (one cup) bottle of 7-7-7 NPK can be made by the addition of 4 ounces of concentrated nitric acid, 1 ounce of 85% concentrated phosphoric acid and 1.5 ounces of concentrated (50%) caustic potash (lye). That is what the fertilizer already contains, mostly pH neutralized.

The nute amounts in the fertilizer completely swamp the acid. Handling the acid is mostly psychological due to the danger, but it is being neutralized by the time it gets to the plant. It is not much different to table salt, One 2 ounce salt shaker contains the neutralization products of almost 2 ounces each of concentrated caustic lye and concentrated muriatic acid. But the salt is food grade and perfectly edible in moderation with no hazard.

    Bookmark   April 18, 2014 at 2:40AM
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Thanks again
I just got home, copied your post. That is interesting that the Fertilizer is just salts or acids
I am going to mix 2 tablespoons phosphoric (half what I have been), whatever that weighs in grams (10-11 per tbsp, I think), into a gallon of water and use 1/4 tsp instead of 1/8 tsp per qt (I will weigh that out in grams).
Also Like You Said, I am going to mix a gallon of that at a time. That way I can cut down on the itty bitty measuring spoons/amounts and the mixing and mixing. Weaker concentrations, bigger measures and bigger mixes..easier to handle, easier to measure. I am also going to increase my fert to 20-20-20
I learned very many things on this thread. I am grateful to you for sharing all this great information.
Thanks Again Now I have an idea of what all this is about :)

This post was edited by lucky123 on Fri, Apr 18, 14 at 22:19

    Bookmark   April 18, 2014 at 10:16PM
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PupillaCharites(FL 9a)

Sounds good. Don't go with the equivalent of 20-20-20 right off the bat since you've been using 7-7-7, since it is nearly triple, The right strength of fertilizer is a re-iterative process to refine, and almost anyone with lots of experience in this forum will probably agree that starting off at full strength does not always help and can burn out the plants. I don't know exactly how you are doing this, but if it is a potted African Violet where water evaporates each day or so and you reirrigate it, putting in full strength can lead to evaporation of the water and salt buildup well beyond the amount you are putting in. The is because the dissolved salts don't evaporate into the air, only the water does. If you are not careful things can turn into salt flats where nothing grows. IMO start gradually and pay close attention to the plants' response. More is definitely not always better. Plants don't have mouths, so it is electrical/osmotic interaction going on at the roots, and the more salt there the more the plants can get stressed if the concentration starts accumulating. Many of the published irrigation ppms refer to recirculating systems where so many gallons are being used or perhaps so many plants feeding, that roots aren't subject to accumulation. That's why a little experimentation is best. The adage is you can always add more later, but you can't take it back...

    Bookmark   April 19, 2014 at 1:50AM
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Everything is already looking better. I have been using fish emulsion in the new phosphoric mix for the last 2 weeks while I figured out what you said..
The AV's have perked right up so I will be careful about fertilizer. I have to adjust everything to the new PH. It is having a dramatic effect without fertilizer, I think
My PH is 8.5+ close to 9 and my plants did alright for about a year and a half on that, then showed signs of nutrient lockout, stunted growth yellowing, bug and disease problems ..various ugliness But I was still surprised at how much a simple PH adjustment greened up and firmed limp foliage. Better living through Chemisty :)
Thanks And Double Cheers for all the help you have given
Much Appreciated!

    Bookmark   April 19, 2014 at 7:15PM
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