Poor Man's Pfertz Dosing (PMPD)

Poor Man's Pfertz Dosing (PMPD)
By Dan Enright​

Preface:

This piece of writing is intended as an interactive thread as much as it is an article. It is intended to be an examination of the pfertz line from top to bottom, with an emphasis on accurate reproduction and the cost of nutrients. I intend to update it for accuracy, correct any technical issues as they arise, and partake in any dialogue on the subject. I hope this to be the first of a series of discussions deconstructing various fertilizer brands, and their implications within the planted tank.

As a brief disclaimer of sorts, I can definitely say that this is all being written for the DIY inclined. Whether pfertz, ADA, Seachem, etc. every company understands that there will be those, both hobbyist and competitor, looking to deconstruct and recreate their products themselves. Their products are for those who do not feel comfortable or are otherwise not inclined to mix their own fertilizers. I encourage those who do not feel that they can work responsibly with any of the compounds mentioned within this article to continue buying premixed fertilizers.


The Short Version:

This section is for anyone who wants Pfertz fast, no questions asked. What follows after is the longer explanation that allows for some of the technical details. Any of these numbers can be halved, quartered, doubled etc. to meet your needs.

The ingredients for each bottle are listed below; simply add the listed weight to half the volume of distilled deionized water, then top off to 1L and stir. It may take some time stirring (or some gentle heat; warm not boiling) to get things right. For pfertz [N] it may be advisable to get the urea and potassium nitrate as a solution in separate volumes of water, then combine and top off.

Pfertz [N]:
KNO3 (Potassium Nitrate): 61.27523782g/L
CH4N2O (Urea): 19.3193426g/L

Pfertz [P]
KH2PO4: 19.17446678g/L

Pfertz [K]
K2SO4: 43.97633951g/L

Pfertz [M] is not covered here as it is far more difficult to reproduce. The reasons for this are covered later on.


On Pfertz and its Content Labeling:

Pfertz outlines its nutrient concentrations as a guaranteed analysis. By law these numbers have to be accurate. The derivatives for each of these nutrients are not required listing as far as I have been able to determine. At a glance, the analysis does not contradict the ingredients listed. This lack of contradiction does not negate the possible use of other compounds to achieve the same guaranteed analysis. I suspect as discussion develops, better insight as to regulations and labeling will surface.

At this time, everything I am writing is based on the assertions pfertz makes about its own product, from its own site. In the future there may be some sort of analysis done, but for now the scope is restricted to statements made by the company. None of what I am posting is more than information derived from what pfertz has been required, or chosen, to release about its own products.

The math behind this project was very interesting. I started with the presumption that all measurements had been given with correction for specific gravity. It turns out that the pfertz site did not make this consideration, and simply calculated the presence of their nutrients as if everything being added was the same density as water. Other deviations from the possibility of actually achieving the analysis given with the listed compounds are noted in the respective sections. For any of my own calculations, I am more than happy to share them. I would include all of them here, but it would result in an article several times this length.

Macro Analysis:

I am starting here with the macronutrient analysis for the [N] [P] and [K] bottles. These will be the products most easily examined and reproduced. Mixing comparable micronutrients is a task far more difficult and expensive, one being on the scale of more commercial than private aspirations. This being an article for the hobbyist, I will leave micros as a topic of brand comparison and dosing.

It should also be noted that there was incongruence between the listed K+ on the site and the K+ that is forcibly added through the above levels. This issue with K+ shows up in every product involving potassium as its base, aside from pfertz [K]. These contradictions sometimes blatantly violate what is possible given the atomic weight of the compounds listed. As such, the topic of K+ is a bit hit and miss. It should not effect any other outcomes outside of the KNO3:urea ratio in pfertz [N], however it does leave a good number of questions unanswered. Hopefully some of it can be answered in the following thread discussion.

For all of the information on the contents of pfertz, the ingredient labels can be found at: http://www.pfertz.com/analysis.html


Pfertz [N]:

Pfertz [N] has a label for its product listed as follows:

Nitrogen [n] (500 mL and refills): 1.75 - 0 - 5.0

Total Nitrogen (N): 1.75%
Available Phosphate (P2O5): 0.00%
Soluble Potash (K2O): 5.00%

Derived from: Potassium Nitrate, Urea

While the nitrogen is most accurately given as N, by the time the product is broken down, a more accurate and hobbyist friendly analysis would be:

Total Nitrogen: 1.75%
(N) KNO3: 0.848899026%
(N) CH4N2O: 0.901100974%
Total N Expressed As NO3: 7.746907734
PO4: 0.00%
K: 4.150563694%

From the above, these numbers were derived as concentrations for:

KNO3 (Potassium Nitrate): 61.27523782g/L
CH4N2O (Urea): 41.50563694g/L

Mixing up a batch of your own may be a little tricky on this one. I am not sure as to the compatibility of KNO3 and urea in stock solutions. A good method would be to dissolve both thoroughly in separate measures of DI H2O, and then combine them. Hearing from someone with urea around that can test the stability of this compound would be helpful. Alternatively, the same dosing level of N can be reached through a weight of 126.3185171g/L KNO3.


Pfertz [P]

The phosphate portion of pfertz dosing was significantly easier to figure out than the [N] product. While the derived K+ from necessary KH2PO4 was off according to both my own and APC’s Fertilator calculations, it will not effect the conclusions I have reached about the required KH2PO4.

The given analysis on the pfertz site for this product is:

Phosphorus [p] (500 mL and refills) 0 - 0.35 - 0.25

Total Nitrogen (N): 0.00%
Available Phosphate (P2O5): 0.35%
Soluble Potash (K2O): 0.25%

Derived from: Monopotassium Phosphate

In a more helpful format, it would be listed as:

Total Nitrogen (N): 0.00%
PO4: 1.338147875%
K+: 0.207528185%

The necessary KH2PO4 to achieve the given level of PO4 would be 19.17446678g/L. Mixing this product would be as simple as adding the compound to a little DI H2O and topping off to 1L. Naturally this level can be adjusted for batch sizes and rounded as scale accuracy permits.


Pfertz [K]:

This product was by far the easiest to work with of the pfertz line. Plain K2SO4, and a K2O listing of 5.1% (4.233752% K+) made it all straight forward. After dealing with the last two, it really made me wonder whether the K+ was listed correctly, but the given information is all we have to work with. The necessary level of K2SO4 works out to 42.337523/L, and mixing it can be done precisely the same way as mentioned in the phosphate section.


Macro Dosing:

So what sort of nutrients does this mean for your tank? The pfertz site doesn’t really tell you what sort of nutrient levels are achieved through their method of dosing. Their analysis also leaves confusion as to what levels of K+ are achieved. As such, both implied levels (DIY and true pfertz) of potassium will be shown, as well as the rest of the results of dosing the pfertz line.

Given the instructions for the product, we will be looking at a high tech dosing routine at 7x a week, 1 pump per 10 gallons per product at 1.2ml/pump. The extra pump per day will be presumed to be as part of the 7 day a week schedule as the 7th day, allowing for a 6 day dosing plan with the typical resting day before water change.

In accordance with the above schedule, and nutrients based off both the site and my own calculations:

NO3: 17.19074ppm
PO4: 2.969411ppm
Pfertz Line K+: 16.34168352ppm
PMPD K+: 17.79787ppm

So despite some small deviations in K+ and N source ratios, the PMPD macro solutions should be very reasonably close to the brand version.

Nutrient-wise, these levels of dosing aren’t too bad. These levels are comparable to a lot of current dosing recommendations, and are not likely to become limiting too quickly. Pfertz macronutrients have shown to work in a number of planted tanks, and the nutrients reflect as such.

Continued...

 

...Continued

Micros:

I’ve put micros on their own for the reasons mentioned earlier. There will be no breakdown on how to mix up a batch of micros, since it would require making about 100 bottles with a rather expensive scale to get any accuracy. Besides that, the issue of keeping 100 bottles stable for the years it would take a hobbyist to dose this solution is something that inclines me to purely deal with the result of dosing their product within the column. The site lists elemental properties in a convenient form; as such I will keep this section to pure dosing results. Here are those numbers, presuming the same dosing routine as in the macro section:

B: 0.011317131ppm
Co: 0.000443809ppm
Cu: 0.000110952ppm
Fe: 0.119828443ppm
Mn: 0.015089508ppm
Mo: 0.001775236ppm
Ni: 0.000110952ppm
S: 0.009541895ppm
Zn: 0.00097638ppm

While micronutrients aren’t my specialty, nothing here seems too far out of line. The iron could be higher, but it’s definitely not insufficient. I think the cost analysis up next will be a bit more telling in terms of criticism.


Pfertz and Cost:

The current running price for a complete refill of pfertz ([N], [P], [K], [M]) runs $107.99 right now. On their own, each of these jugs are priced evenly, so this cost can be evenly divided for the NPK line. One jug being about 1892ml, the cost is effectively $14.27/L.

By comparison, one can pick up the same quantity of compounds for 1L each of N, P and K of PMPD for about $0.975 plus $0.280 if you want the equivalent sort of micro dosing from CSM+B, and something like $0.210 for DI H2O. End cost is about $1.47/L ; a hair more than 1/10th the price. Add the fact that you’re not paying to ship water weight, and you’ll be saving even more.

If you want something other than CSM+B for micros, Seachem’s Flourish is a comparable price at $27/2L, usually around $30-$35 in stores, but without the cost of shipping. Flourish also tends to show higher nutrient concentrations: http://www.aquarticles.com/articles/plants/Podio_Fertilizer_Comparison_Chart.html

All pure cost criticisms aside, Pfertz doesn’t do too bad in bulk considering costs. Having mixed my own stock solutions, and knowing the time it takes, the markup isn’t completely unreasonable. Packaging probably runs around $5 each for the big ½ gal jugs, total nutrients and water we’ll say $1 given their bulk volume, leaving somewhere around $10/unit for covering the rest of costs and wages.

The small bottles, on the other hand, don’t seem to be worth the price. Costs there are about $27/L and you can bet a good chunk of it is in the fancy little bottles. For those prices, it’s probably worth it to measure the stuff out, or alternatively find cheaper pump bottles and buy bulk off the start.


What Now?

Examine, discuss, rant, plan ahead. This is to be the first of a few large posts and articles examining various brands of fertilizers, the nutrient parameters they achieve, and their costs. At the end I’d like to culminate everything with a comparison of multiple brands. I’d like to see this one discussed for a while, corrections made, and the pfertz line figured out a little better. Once things quiet down and I feel like doing this all over again, I will work on the next post. If you would like to reproduce this article somewhere, let me know and I will edit it into something that looks more like a stand-alone piece.

- Dan (Philosophos)

 

Damn you and your trolling, Tom

Since you suddenly can't handle CaCl2 without wondering why it burns later, we'll remove all the sharp objects from your home

Seriously though, I've tried telling people how to dose standard EI; zero interest when there's brand loyalty. The same people perk up if you tell them how knock off their favorite brands. Once you've got a couple lb's of all the necessary ferts sitting around, tinkering is far too easy. I was thinking maybe TPN+ and Seachem next, with ADA knockoffs in the subscriber section based off of your analysis.

Here's hoping this helps the DIY interest. Even if I want to start my own brand, I hope that those hobbyists with real interest deconstruct it.

-Philosophos

 

I've read James's work; it's nicely done. My one point of concern with it is the issue of getting KH2PO4 to play nice with all the micros. I end up with some very instant, nasty precipitates from even the slightest contamination between KH2PO4 and micros. Part of the TPN article would be trying James's method and exploring the interaction.

Gerry, I think we're all waiting for that roll of micros with baited breath. I'm on the verge of just mixing a big batch of my own micros once I run out of flourish to supplement CSM+B with.

-Dan

 

No... but I found out about him after Ben Stein once stared directly at the camera and swore on my immortal soul that he had no foreknowledge of the answers to the questions he was given. Do you know how much that messes a guy up?

Yes, I've noticed. If you hand them your own bottle they're often very willing to give it a try, if you give them their own brand at 1/10th the price then they're a little easier too. This is how I've gotten good responses with my own efforts.

I do when it hurts the hobby. I begrudge ADA for selling its near-useless liquid product, and I said something when Tetra was selling 10mg/M^3 of KNO3 at $5/500ml. In this case, I don't decry the producer but I support the freedom of knowledge for those willing to try making it with a little help.

Ya, and the worst of them are almost like Nigerian 419 scams or Scientology. I could think of some harder hitting, closer to home examples but I'll leave it at the obvious. I support flushing this sort of thing out of people's head when I can; all of us do it, and I think the first step is accepting when we are victims of it.

We'll have fun with this part some time on an off-topic post... I'll see you the rights and raise you a Russel's teapot.

I agree, and I think that the actual effort to do DIY doesn't take very long if you follow canned instructions. Some of us like taking it a step farther and developing the hobby. This article is geared for both.

Most definitely, there are people who want this. There are artists and connoisseurs that exist separately from one another. I appreciate a good boreaux, but I haven't bothered making my own wine. I believe Tom was supporting his right to buy a bottle of thunder bird as a reputable vintner in this case

In any case, your criticism is appreciated. I'd like to see more posts like yours made about this thread. I appreciate everyone's kind words so far, but the next step so often starts with contradiction. Serious peer review and the work of contemporaries is so vital to improving any new concept.

-Dan

 

I'll keep that outline method in mind Tom. This first time around does seem a little intermingled with things that a new hobbyist probably wouldn't care about. If the whole of the US hasn't heard of specific gravity while drinking so much beer, there clearly isn't an interest in it.

-Philo...Da... you know, I really need to just get a signature.

 

The incomprehensible math will hopefully become more common place with time. I think there's some formulas that can be dumbed down for the average person, with expanded versions for them as they grow. Things like basic nutrient:compound ratios need to be more common place.

Hmm... maybe a cross wrapped in bacon

 

That baconaise is making me a bit queasy just looking at it. Something makes me think that it's mostly from that weird bacon-like taste that soybean oil gives to cream dressing.

Oh, I did a little breakdown work detailing what individual pumps and other levels of spec dosing will do. All measurements are in ppm:

Single Pump:

1 pump N:
Total NO3: 2.455819821
Total PO4: 0
Total K: 0.871653328

1 pump P:
Total NO3: 0
Total PO4: 0.353501271
Total K: 0.025554445

1 pump K:
Total NO3: 0
Total PO4: 0
Total K: 1.616732962

Based off of that, here's what the various dosing instructions found here will result in:

"The Simple Solution"
Dose nitrogen [n] 2x per week @ 1 pump per 10 gallons.
Total NO3: 4.911639642
Total PO4: 0
Total K: 1.743306656

"The Medium-Tech Solution"
Dose nitrogen [n] and [m] 2-4 times per week @ 1 pump per 10 gallons.
Same as above for 2x, 4x would be:
Total NO3: 9.823279285
Total PO4: 0
Total K: 3.486613312

"The High-Tech Solution"
Dose all liquid fertilizers 5-7 times per week @ 1 pump per 10 gallons.
5x a week:
Total NO3: 12.27909911
Total PO4: 2.121007625
Total K: 12.59525812

7x a week:
Total NO3: 17.19073875
Total PO4: 2.969410675
Total K: 17.63336137

And then of course there's the water change double dosing that'll add 1 pump extra of each respective nutrient that you dose on to the total.

Obviously recommending N but no K+ is a bit backwards. Has anyone used pfertz lower spec dosing and had K+ issues?