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PMDD: Doses

A consensus has emerged on the Conlin and Sears
PMDD formula: mix with water to make a 1/2 liter solution,
       1 tablespoon chelated trace mix
       1 tablespoon MgSO4+7H2O
       2 tablespoons K2SO4
       1 tablespoon KNO3  (may vary, depends on nitrate)
        [Thanks to Steve Turner and Onis Cogburn for mix-fix]

Now how about dosing? Does anyone have any comments
on these revised sections of my previous "PMDD: Sources and
Doses" post?

 H)  How to dose PMDD

 1)  So, why not just pile on the PMDD so you're sure you have
     more than enough of each of its nutrients? Because:
     - Dosing just a little bit too much PMDD can lead to a nutrient
       excess that will give unwanted algae a foothold. :-(
     - Too much is not the best for your fishes' well being.
     - Too much of specific nutrients can be injurious to specific
       plant species.
     - Way too much and the excess can actually inhibit a
       plant's ability to properly utilize nutrients present. How's
       that for contrary!

 2)  No question, many consider determining PMDD dosages
     an art. The reason for this is people's requirements
     for both "amount" of nutrients and "ratios" of nutrients
     to one another can differ. Why? Well, here are some things
     that make the amount and ratios of nutrients you need
     somewhat unique to your situation:
     - Nutrients already in your tap water and how often
       you do partial water changes.
     - The number of fish you have and nutrients generated
       by them (this especially impacts N (nitrogen)).
     - How much you feed your fish. Overfeeder? Minimalist?
     - Fertilizers you may use in your substrate that could
       leach into the water.
     - The density of plants you have. More need more.
     - The density of plants you have. More need more.
     - The kind of plants you have. Some rely more on water
       bound nutrients, some derive more from the substrate.
     - "High Tech" supplements like CO2, lots of light, etc.
       [Thanks to Pat Bowerman for input]

 3) As a starting point, here's a three point plan for setting
    an PMDD doses.

    a)  The amount or "size" in ml (milli-liters) of your daily
        PMDD dose should be eventually governed by monitoring
        Fe (iron) levels that accumulate and equilibrate in your
        aquarium over a period of time (more on this later).

        But, to get started, for each ten gallons, try around
        1/12 ml of PMDD a day (roughly 2 drops). A 29 gallon
        tank would then get 1/4 ml a day (roughly 6 drops).
        If you don't do many partial water changes, dose less.

        If you have a "high tech", densely planted, CO2 injected,
        VHO lit tank, you might want to double the dose to
        1/6 ml of PMDD per 10 gallons a day (roughly 4 drops).

    b)  Most of the PMDD nutrient ratios set by Conlin and Sears
        will work for a variety of conditions. PMDD has been
        deliberately formulated so that if aquarium Fe concentration
        is proper, other nutrient concentrations should fall into place.
        Really, the only common exception to this is NO3 (nitrate);
        you may need to tinker with the ratio of KNO3 to other
        PMDD ingredients. Adjusting this ratio will eventually be
        governed by NO3 levels that accumulate and equilibrate
        in your aquarium over a period of time (more on this later).

        To get started, if you have around 5mg/ltr of natural
        NO3 already in your aquarium, initially use the standard
        1 tablespoon KNO3 per 1/2 liter PMDD mix.

        If your natural NO3 is much higher, initially don't add any
        KNO3 to your PMDD.

        If you have next to no NO3, you might initially boost the
        KNO3 to 2 or even 3 tablespoons per 1/2 liter of PMDD.

     c) Lastly, as you go along, you'll need to monitor buildup
        of Fe and NO3 in your aquarium and watch how plants
        and unwanted algae respond. As each daily dose
        adds nutrients, a portion will accumulate
        until eventually you'll reach an equilibrium level.
        This ramp up and stabilizing process will take
        awhile (weeks) to occur. Be prepared to adjust your
        dosage size and KNO3 ratio as you gather feedback.

 4)  The specifics on Fe

     a) Consensus is to dose PMDD so that you accumulate
        and maintain around 0.1mG/ltr (0.1 milli-grams/liter or
        0.1 Parts Per Million) concentration of Fe (Iron) in
        the aquarium. Exceeding 0.2mG/ltr of Fe seems to
        be counterproductive.

        With the dosage size recommended part 3, you should
        see Fe levels slowly ramp up. Eventually, Fe you add
        will equal what's depleted from plant use, water changes,
        etc. Again, fine tune your dosage size so at that
        equilibrium point, your Fe is around 0.1mg/ltr.

     b) So, what if use of laterite raises your Fe levels too?
        I'm not really sure though I use laterite, limit PMDD
        doses to keep overall Fe levels below 0.1mG/ltr, and
        still achieve ample nutrient concentrations.

     c) Suspecting that to much Fe can promote algae growth,
        Steve Pushak notes he only adds sufficient Fe to keep
        plants growing without symptoms of Fe deficiency or
        chlorosis (yellow or pale leaves), a level that may fall
        under 0.1 mG/ltr Fe. He has found Salvinia to be a good
        indicator plant for Fe dosing.

     d) Oh, SeaChem, Red Sea, Tetra, Dupla, Hach, LaMotte
        all make Fe test kits. Prices and ease of use very
        widely. At the time of this writing, there has been
       some controversy as to whose will accurately measure
       chelated Fe; make sure yours will. Try:
        "That Fish Place"; 800-733-3829 or
        "Pet Warehouse";   800-443-1160.

 5)  The specifics on NO3

      a) Consensus is a good target for aquarium NO3 is
         3 to 5mG/ltr (3 to 5 PPM).

         Remember, adjust NO3 by varying the amount of
         KNO3 you add to PMDD, don't adjust dose size. In other
         words, the daily size (ml) of the PMDD dose is determined
         by desired Fe levels. The ratio of KNO3 to other PMDD
         ingredients is what you vary to bring NO3 levels to where
         you want them.
         [Thanks to Mark Fisher for input

     b)  As time passes, you might notice that as PMDD
         begins to balance things out by providing other
         nutrient components, your levels of naturally
         occurring NO3 will fall (it's being used). You may then
         have to increase the KNO3 added to your PMDD to
         maintain the 3 to 5mg/ltr NO3 concentration.

         Still if you do ultimately reduce or eliminate KNO3
         from the mix, don't worry about having also reduced
         the K. The K2SO4 seems to provide enough.

      c) Many of the folks that make Fe test kits also make
         ones for NO3. Check that they're accurate in the
         5mg/ltr range.

 6)  I don't know what a good target for K (potassium) is.
     It turns out to be really difficult to measure anyway.
     Since PMDD is rich in K, and I've read you can have
     a fair bit of excess K without harming aquatic life,
     I wouldn't worry about it.

 7)  PMDD has no P (phosphate). According to work by
     Sears and Conlin, having the P in N-P-K as your
     limiting major fertilizer factor helps reduce algae. Of
     course plants require some P (.02 mG/ltr a good target),
     but you'll no doubt have more than enough supplied by
     fish food and waste.

     Most terrestrial plant fertilizer supplements have a
     lot of P. They may also have N in the form of NH3/NH4
     (ammonia/ammonium) or CO(NH2)2 (urea), both quite
     toxic to fish unless dosed very very carefully. That's
     why the advice to not use otherwise fine products like
     Miracle Grow.

  8)  Why daily PMDD doses rather than a weekly mega-dose?
       -Some constituents of PMDD are not terribly stable
        (like chelated Fe) and may loose some potency in the
        aquarium over the course of a week.
       -You avoid concentration "spikes" that fish might
        not appreciate.
       -Even if PMDD nutrient ratios aren't perfect for your
        situation, you will have at least some of whatever
        your limiting factor is available each day.

   9)  Most drug stores sell droppers marked in mL for
       dispensing medicine. The 2.5 to 5mL sizes work
       great for metering out PMDD. Oh, when dosing,
       I'd first shake the bottle in case of settling, then
       try to stir the PMDD slowly into the aquarium so
       fish don't get hit with a "chemical cloud".

       Also, if you have a small aquarium and find
       fraction mL doses tough to dispense, you can dilute
       the PMDD and adjust dosages accordingly. For example,
       use twice as much water to mix up the PMDD, double
       your dosage size.

 I)  Some of my dosing experience

    1) Did I follow my own advice and go slow . . . no. <g>
       I initially dosed with 1.7 ml PMDD a day in my
       45 gallon tank (40 gallon water column). I changed
       25% of my tank's water each week. If you assume
       no Fe depletion (a poor assumption but good for
       establishing an upper bound) my Fe concentration
       would have eventually leveled off at 0.4mG/ltr. Too
       high! So, once Fe reached 0.1 mG/ltr (took
       about 2 weeks at the 1.7 ml dose), I reduced my
       PMDD dose to a little over 1/2 ml a day.

       My plant growth really improved.    :-)

    2) Now you've read this and want to "jump start" things
       too. True, I did find for the initial first few weeks
       I could safely double or triple dosage recommendations
       made in part 2 of "How to Dose PMDD". The problem is
       you've got to keep very close track of Fe and NO3, and
       then remember to roll back your dosages once you
       reach your target levels. If you don't, at best you run the risk of
       becoming an algae farmer, at worse your plants and fish
       will suffer.

Tim Mullins - Pittsburgh