# PMDD: Panacea or just plain wrong?



## MiamiAG (Jan 13, 2004)

OK,

As the title implies, some view PMDD as a cure all whereas other view PMDD as simple incorrect. Where do you stand? I'll give you my take.

First, some background. PMDD (Poor Man's Dosing Drops) is based on the famous Sears/Conlin paper as a way to control algae (the paper will be in the library section in a few days). Originally, PMDD stood for Poor Man's Dupla Drops as Dupla as the de facto standard back then. However, once the paper was posted to the APD, comments surfaced about tradename issues so the name was changed.

On its face, PMDD seems to rely on Liebig's Law of Minimums whereby limiting one essential element will result in algae control. Inherent in this logic is that plants will be able to withstand the essential element limitation better than algae and, thus, survive instead. Of course, the essential element that is limited is PO4.

Many experienced aquatic gardeners did not take PMDD literally. We all knew very well that phosphorus is an essential element for the proper growth of plants. Many of us had been running PO4 deficient tanks that required us to add PO4. I remember discussing with Karen Randall on FISHNET whether we should tell this to newbies that typically had extremely high PO4 levels. The last thing we wanted was for them to add more PO4.

I did not interpret the PMDD method to mean PO4 must be zero as that would not make sense. I read into the underlying meaning that IMO is "competition". In other words, I can add an excess of nutrients except for one (PO4). That one must be provided so that sufficient exists for the plants, but there is no excess. In so doing, you are providing the minumum requirements for the plants, thereby giving them the edge in the competition with algae.

I would tie this into the Estimative Dosing method popularized by Tom Barr, our very own Plantbrain. Again, IMO, I think the reason we don't grow algae but instead grow healthy plants with the Estimative Dosing is "competition." I do not buy the allelopathy discussions that have gone on in the APD lately. The large exchange of water would dilute such phytochemicals rendering them ineffective.

Your thoughts?


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## plantbrain (Jan 23, 2004)

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## Rex Grigg (Jan 22, 2004)

I see it all the time. Some shiny faced new person finds the PMDD study and thinks it's the "be all to end all" and they just know that you have to totally eliminate any traces of PO4 in their tank to get rid of their algae problem. I'm not a fan of PMDD at all. I hate one size fits all approaches. Most of the time they end up being one size fits some at best. Many of these new people also have read just enough to know the the more light the better and that soil is a good cheap substrate. So they jump on 4-5 watts per gallon and proceed to dig some top soil from the lawn and wonder why they have problems. Most of them also have learned about DIY CO2 and have a liter or two of mix running on their 55 gallon tank.

These same people also find the CO2/kH/pH chart and by just looking at the chart and not reading the reasoning behind it know that if they use pH down they can get their pH down and their CO2 up. Then they discover that pH down has added a lot of phosphates to the water so they "discover" the Sears and Conlin paper and PMDD. Have I said I hate the PMDD idea? Well not the idea but the fact that it's so available on the internet without enough warnings.


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## plantbrain (Jan 23, 2004)

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## niko (Jan 28, 2004)

To me PMDD means "cutting corners" rather than "have a one step solution". 

Adding Fe/Traces/N/K/P in one step does not make sense to me. In an established tank that has ran for months it is possible to add PMDD that has macros and micros in one bottle. But all parameters of that tank must stay constant. 

I personally add chelated trace mix, N, P, (and may be K) separately.

Some of my plants do seem to suffer from lack of P and N because I keep both of these elements at bay, especially the P. Since I don't use layered substrate it is very obvious that I have to add some N and P along with the Fe/Trace. Luis on the other hand does not seem to have any problems with lacking P or N, probably because of the substrates he is using. I heard that he thought some of his plants were not doing as well as he thought they should but I don't know what he meant, his plants look extremely good.

It does seem that excess P is what will cause algae, but low P and high N is also a problem. I can very much say that low P and excess N is the way to staghorn algae. 

Overall my opinion is that P has to be limited but still present. N should be much higher but not too high. Pretty much "keep the ratio 1 P : 10 N". Also - the P and N could be unmeasurable but the tank could still look great. It's my speculation that in that case the P and N are in the correct ratio just in minuscule amounts, much less than our tests can catch. 

The opposite situation - higher P, say 3 and N of 25-30 is not good either despite the "good ratio"- sooner or later I see the algae starting to creep in.

So according to me using PMDD containing all the nutrients is not a good solution.

(An interesting observation that I have shared with many people was that extremely high P levels - 40+ ppm - inhibit the growth of both plants and algae. Certain plants do thrive though - Bolbitis, Pellia, M. matogrosense green)

--Nikolay


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## Jim Lockhart (Jan 27, 2004)

*PMDD: Panacea or just plain wrong?*

When it first came out , I think the PMDD idea was a big step forward in understanding the nutrient management of a planted tank.

It emphasized the need for addition of traces and I personally had some success controlling algae with the method. However I did see some limitation in plant growth rates because I allowed N or P to become limiting.

However with light at 4+ WPG, and 30ppm of C02, the recipe needs to be updated. The limitations can occur very quickly in this scenario.

As in Niko's comment, some tanks may be able to do well with the proper N ratios even at very low un-testable amounts, but tanks 'on steroids' will wipe out those levels very quickly.

So you have to know your ingredients before you mix your recipe.


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## naman (Nov 12, 2005)

Why everyone talking about PMDD only? Anybody tryed to do Pure Man's Tropica Master Grow? Proportion of Fe-Mg, Mg-K... in PMDD very diffrent of that in the TMG. Any considerations?


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## BryceM (Nov 6, 2005)

The thing that killed me was the incredibly small dose suggested in the original Sears-Conlin paper. The following is from the post on thekrib.com's site, 'Appendix A'

_1 Tbsp (~9g) Chelated Trace Element Mix (7% Fe, 1.3% B, 2% Mn, 0.06% Mo, 0.4% Zn, 0.1% Cu, EDTA, DTPA)_
_2 Tsp (~14g) K2SO4 (potassium sulfate)_
_1 Tsp (~6g) KNO3 (potassium nitrate)_
_2.5 Tbsp (~33g) MgSO4.7H2O (fully hydrated magnesium sulfate, aka epsom salts; omit if already present in trace element mix)_
_300mL distilled H2O_
_0.5mL 9M HCl (optional)_
_...*Add enough mix to the tank every day* to keep the Fe level at about 0.1ppm (the exact amount will have to be determined by experimentation, but *3mL per 100L tank water is about right for a tank with rapidly growing plants*). Measure nitrate levels regularly, and adjust the amount of KNO3 in the mix to maintain 3-5ppm (this step is fairly important). Those concerned about adding nitrates to their aquarium can dose the KNO3 separately, omitting it initially and adding it later as required to obtain the desired concentration._

With their formulation it would take 100 days to use 1 tsp of KNO3 in a 100L tank!

So what did I do being a dumb newbie? Set up 4 wpg, CO2, tons of stem plants and dosed per the above recommendations. Result - everything did ok for a few days and then all the plants started to show severe signs of deficiencies. After much recipe tinkering I'm now doing 1.5 tsp KNO3, and ~6ppm PO4 via fleets per week in a 46 gal. Things are better, but algae issues continue. Am I missing something here or is the suggested dose of PMMD about 20x lower than EI? Having started with their ideas, the quantities of ferts that I'm pouring in now seem enormous.


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## plantbrain (Jan 23, 2004)

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## BryceM (Nov 6, 2005)

So Tom, a question that I've been thinking about. You indicate in your report and other places that NH4 induces algae. Does this mean that a large fish load (more NH4) contributes to the algae problem? Is there anything you can do in a heavily stocked tank to compensate? I prefer tanks that are heavily stocked, but prefer the algae even less.


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## RTR (Oct 28, 2005)

PMDD was based on an incorrect assumption, but it happened to work for many folks due to the "standard" conditions and proceedures in use at that time. Therefore it was then seen as valid. The holes and issues did appear until changes in techniques and lighting showed it to a special case application and not a valid broad theory. 

We could offer substrate heating as another failed or invalid theory, but one which never achieved wide acceptance. It too is a special-circumstance application.

EI is our theory of the day, and certainly seems to be broader in its reach than what had waved as THE theory previously, but TB is, I hope, not going to retire on that, nor will others. Perhaps we really will continue to develop or knowledge, that is certainly hoped. Information and knowledge are never static. Stasis is dead and boring.


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## plantbrain (Jan 23, 2004)

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## plantbrain (Jan 23, 2004)

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## naman (Nov 12, 2005)

Sears&Conlin made Micros, dont Macros (NO3+PO4) !!! NO3 is just for "insurance". 
Their dosage is correct, but... Search for "Nerd stuff on calculating aquarium PMDD constituent concentrations." at TheKrib, where math-boy made formula based on that fact that with weekly water changes concentration of ferts is reducing. This You must take in consideration when calculating dose. 
Next, they suggested that Fe=0.1ppm is ok, but folks on the web saying it is not enough! As I am (tested 1.5 years). In densely planted aquaria you have to dose for a 0.3-0.7ppm. When plants consump and Fe dissipates concentration would be ~0.1ppm. The same 0.1ppm, but with fare different consequences - no Chlorosis! 
As for macros NO3+PO4 - you definitely must dose them too as in EI system! Like Amano does. Look at APC for PJAN's step lightning method and brows for a PO4 dosage. *Very *good explanation Why to dose more/less. 
Why NO3O4 is 10:1 or 15:1 - read "Redfield ratio", by Charles Buddendorf [http://www.xs4all.nl/~buddendo/aquarium/redfield_eng.htm]. Science Only. Remember about NO3O4 disproportion in fish food. 
Sorry for my pure English.


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## hoppycalif (Apr 7, 2005)

naman said:


> Sears&Conlin made Micros, dont Macros (NO3+PO4) !!! NO3 is just for "insurance".
> Their dosage is correct, but... Search for "Nerd stuff on calculating aquarium PMDD constituent concentrations." at TheKrib, where math-boy made formula based on that fact that with weekly water changes concentration of ferts is reducing. This You must take in consideration when calculating dose.
> Next, they suggested that Fe=0.1ppm is ok, but folks on the web saying it is not enough! As I am (tested 1.5 years). In densely planted aquaria you have to dose for a 0.3-0.7ppm. When plants consump and Fe dissipates concentration would be ~0.1ppm. The same 0.1ppm, but with fare different consequences - no Chlorosis!
> As for macros NO3+PO4 - you definitely must dose them too as in EI system! Like Amano does. Look at APC for PJAN's step lightning method and brows for a PO4 dosage. *Very *good explanation Why to dose more/less.
> ...


The "redfield ratio" refers to the ratio of N and P, not nitrate and phosphate, and it has been demonstrated not to be relevant to algae issues. It is just one more of the solutions proposed and found wanting.


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