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what is PMDD all about?

Discussion in 'General Plant Topics' started by danski, Oct 7, 2007.

  1. danski

    danski Junior Poster

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    and should i be using it? im currently using E.I but im just about out of phosphate and need to re-order. im thinking maybe using the PMDD but have no clue as to using it. do i still dose macros and micros or just that? and how much? or should i just stick to dosing nitrates and phosphates one day and micros the next? thanks...dan
     
  2. VaughnH

    VaughnH Lifetime Charter Member
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    PMDD is not what you should try. It was one step towards good fertilizing made several years ago, but before the importance of phosphates was recognized. You need to get some phosphates - Fleet Enema will suffice until you do.
     
  3. danski

    danski Junior Poster

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    thanks much..i will stick to what i know then...dan
     
  4. FacePlanted

    FacePlanted Guru Class Expert

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    Yes. I would consider PMDD the precursor to more modern techniques such as EI. Phosphate is important. I think it (PMDD) relies on nutrient limitation (of P) rather than nutrient excess. Apparently nutrient limitation doesnt work very well as the algae can use the negligible traces of P while the plants cant. The plants suffer as a result and algae gains a foothold.

    I have used the fleet enema also. It works well. I used maybe 30-40 drops in my 29 gal.

    -Mike B-
     
  5. Tom Barr

    Tom Barr Founder
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    Well, there where a few precursors prior to PMDD:

    http://www.barrreport.com/estimative-index/2386-old-version-1996-1997-list-levels-parameters.html

    Which was namely this:

    http://www.barrreport.com/estimative-index/3209-want-more-accuracy-want-daily-pmdd-style-ei-dosing.html

    Most folks did the second link as they had been doing PMDD prior and then took the rather large leap of faith at the time(you folks have no idea how folks went after me about this issue, it fundamentally disproved/falsified a long cherished hypothesis, but the proof was in the results).

    Since folks where already dosing KNO3, K2SO4, GH, Traces, and many used daily dosing, all that was needed was some PO4.

    So if you wanted to add less and dose with more precision etc and tweak subtle things more, then the above link would work nicely. If that was/is your goal..........

    However, many did not have that same goal. Steve did not do water changes for 6 months, Dave did not do any for 2 years and they used the test kits etc to dose accordingly. That was over a decade ago.

    But it sounded too complex(PMDD with liquids etc and dosing solutions), folks had to test etc.

    I knew that using larger water changes reset my tanks anytime I mess up dosing or made mistakes. So If I did large enough water changes weekly, I could guess or estimate the rest of the week's dosing and simply reset at the end of the week.

    I also knew large water changes help plants, algae do not like them, keeps the tank clean, makes the tank much much easier to prune and clean/work on etc. I knew that most all aquarists know how to do a water change and that requires no chemistry or complex stuff.

    Teaspoons are easy and simple to use vs a scale. I just estimated based on 20 samples, the weights of 1/4 teaspoon and then tried several brands of teaspoons to be sure they where close using a lab scale.

    From there I could get an error range for the teaspoon method.

    When some folks claimed that this was inaccurate and sloppy on another forum some years ago, I lamblasted them because I've already measured the error and know the results, I knew them 10 years ago, long before most of them even kept plants.

    It's irritating when folks make poor assumptions, it's even more so when they obviously have not done the measurements or test to prove their statements which are derogatory and bad mouth other folk's research and methods without any support. I support what I say, try it and test it. Then think about it, then go back and do it again, and again etc.........

    That takes work.

    Regards,
    Tom Barr
     
  6. Carissa

    Carissa Guru Class Expert

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    So what is the margin of error using teaspoons as compared to scales?
     
  7. VaughnH

    VaughnH Lifetime Charter Member
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    If you measure your weight using a precision scale accurate to the nearest microgram are you more accurate than if you step on a bathroom scale? The answer is no, because any accuracy beyond what the bathroom scale gives you is of no value. The same is true of fertilizing. Since we are using the "estimative index" method, we are just estimating the amount of each fertilizer that is needed and dosing that. If we were to weigh out each dose on a microgram accurate scale it would not in reality be any more accurate since there is nothing to gain by knowing the amount with any more accuracy. That's my opinion.
     
  8. Tom Barr

    Tom Barr Founder
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    As what Vaughn mentions, but more specifically, I found a SE of +/- of 0.011 grams.
    A scale that's accurate to 0.01 grams is only a accurate to 0.01 grams, so virtually no difference.

    Still a certain Clown on a certain forum claims that EI and teaspoons is inaccurate vs a 0.01 gram accuracy scale.

    I ran 4 different types of 1/4 teaspoon scales, 20 runs each(which gives about 95% confidence level), normal average type of level KNO3 fills. So a total of 80 test, then run the SD and SE for each of the 4 teaspoons. The SE is 0.011 for 1.670 gram average using a lab calibrated scale in the chem dept.

    This is for Grant's Stump remover. This translates into about +/- 1ppm of NO3 from KNO3 dosing this method. I wrote this going back nearly 10 years ago!

    Other brands, grain sizes etc may vary.........but that's not due to the teaspoon or the user. Nor is the variations is grain sizes ever accounted for on any dosing calculator I've ever seen...........

    So if you use a dosing calculator(I do not FYI), then you can run into issues and assumptions that the dose is accurate based on the calculator.

    Measuring water for the dilution for solutions also adds some error.

    The tank's volume is also another source of error, as well as the test used to measure uptake/nutrient decline in the tank.

    This starts to add up to fair amount of error.

    If the nutrients are on the higher end of non limiting levels, then it will not matter if the error is + or - 5ppm for NO3, or .5ppm for PO4 or 0.1-0.2 ppm for Fe.

    So dosing at higher concentrations gets around a limitation even if mild, and allows you to isolate other issues such as CO2, the most common problem for folks.

    PMDD was around before EI. EI is merely derived from PMDD and is a reduced method. PMDD is merely a hydroponic method minus the NH4 and more diluted concentrations.

    If there were many folks that have been on the web still from this time period, they would say pretty much the same things, however, if not, these new batch of hobbyists think they have (re)invented the wheel again.

    Regards,
    Tom Barr
     
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