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[APD] Re: comparison of PMDD and Toms method side by side please

"Could someone explain in newbie terms what is the main dif between PMDD and
Toms formula, near as I can tell Toms supplements phosphates also where as
the pmdd limits them. I am admittedly a confused planted tank newbie. Sort
of a side by side compare/contrast."


I am going to limit myself to giving you the 10000 foot view as I see it.
The PMDD formula is based on the concept of limiting certain nutrients or
nutrient (PO4) to combat algae. While this has proven to work, it also
limits PO4 to the plants which will obviously not benefit from this. Tom
Barr's method instead is based on providing certain amounts and ratios of
nutrients in order to not limit the plant growth in any way. Algae in this
case is "magically" defeated by the plants themselves... I say magically
because, as I'm sure you have read the recent posts on this topic, we are
still not sure what it is that makes the plants win over algae in this
scenario. But as you said, the main difference is the addition of PO4 and
the recommended levels of nutrients. I also feel there is some difference in
the amount of light used in the PMDD paper compared to Tom Barr's regime, if
I'm not mistaken PMDD was conceived and tested in tanks with less light than
the ones Tom Barr's method is most successful in. I may be wrong however,
it's been a while since I read the paper... I think as lighting is increased
and therefore plant growth is sped up, limiting PO4 will cause
greater/faster effects on the plants than it would if plant growth was

If you are new to all this stuff, as I was coming from a strict history of
low light tanks, I found it easier to not have to worry about finding
chemicals, making mixtures and figuring out concentrations and so forth
initially. I adopted the Tom Barr method, however started off using off the
shelf products. In my case I used the Flourish line (Flourish, Iron,
Potassium, Phosphorus, Nitrogen and Tabs). I had very good results using
these products and switched to the dry chemicals for economic reasons, nothi
ng more. I did not personally find the CSM+B trace mix to be as complete or
effective as Flourish so to date I rely mostly of Flourish for my traces. I
also mix some CSM+B into the trace mix, mostly because I have 5 year supply
of it, at least... I found that by doing this I was able to concentrate on
dosing and finding the ideal levels and ratios that worked best in my tank,
then moved on to "cooking my own".

In the end you have the option of using a few different chemicals or
products for each element, you noted a couple yourself for PO4. I don't
think there is any differences or specific recommendations in one method or
the other as far as which chemicals to use. It's mostly a difference of how
to use them, frequency, suggested levels and other minor differences. Seeing
we have the luxury of having the authors here, I'm sure they will be able to
provide all the nitty-gritty details and any corrections to my explanation.

Hope that helps
Giancarlo Podio

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