WHAT IS THIS PMDD STUFF ANYWAY? The concept of PMDD comes from the Sears/Conlin paper in which it was determined that in planted aquaria which have an excess of all plant nutrients
BUT with limited phosphate, plants are able to outcompete algae. This results is healthy plants
and little or no algae in the tank. The name PMDD is short for "Poor Man's Dupla Drops", a
reference to an inexpensive homemade nutrient program. The beauty of PMDD is that it can be
tailored to the needs of each specific aquarium. It can be mixed to contain any or all required
WHAT IS IN PMDD? 2 Teaspoons (~14g) K2SO4 (potassium sulfate)
1 Teaspoon (~6g) KNO3 (potassium nitrate)
2.5 Tablespoons (~33g) MgSO4-7H2O (fully hydrated magnesium sulfate, aka epsom salts;
omit if present in trace element mix)
1 Tablespoon (~9g) Chelated Trace Element Mix
(7% Fe, 1.3% B, 2% Mn, 0.06% Mo, 0.4% Zn, 0.1% Cu, EDTA, DTPA)
300 ml (1.5 cups) distilled H2O
WHERE DO I GET ALL THIS STUFF? Potassium sulfate is sold as All Green in garden centers. It can also be ordered through
pharmacies. An alternate source of potassium is Seachem's Potassium. Another choice is
KCl, sold as muriate of potash in hardware stores.
Potassium nitrate is sold as stump remover in garden centers.
Magnesium sulfate can be found in grocery and drug stores as Epsom salts.
Chelated Trace Element Mix can be ordered from hydroponics shops or garden centers.
Other ideas for sources
WHAT DO I DO WITH ALL THESE COMPOUNDS WHEN I HAVE THEM? There are several options here.
1) Mix them all together according to the recipe. Shake well. Keep in the refrigerator.
2) Mix everything except the chelated trace element mix. Instead of using CTEM, use a
commercial preparation which contains iron and trace elements, such as Seachem's Flourish,
Schoeler's Natural Gold, Tropica Mastergrow, or Kent Plant Supplement. Add this separately
from the PMDD.
3) Make separate solutions of everything so that you can dose only what you need. Have one
container with only K2SO4, one with KNO3, one with MgSO4 and trace elements. Or use any
other combination which suits your needs.
OK, EVERYTHING'S MIXED, NOW WHAT AND HOW MUCH DO I ADD TO MY AQUARIUM? This is where you have to observe your own tank and make decisions relevant to your own
situation. If you've mixed the PMDD all together, start by dosing small amounts - say, a few
drops per 10 gal, every few days or daily. Observe the plants, keep an eye on nitrate and iron
levels, and watch for increased algae growth. You want to maintain about 0.1 ppm of iron and
5-10 ppm of nitrates in the water. If algae growth is increasing, cut back the dosage. If no algae
is forthcoming, increase the dosage. By trial and error, you will discover what works in your
If you mix up separate solutions, determine what your tank needs. Are nitrate levels where
you want them, but plant growth is slow? Try adding just potassium. Is new growth looking
mushy and transparent? Might want to add iron and trace elements. Are new leaves yellowish
except for green veins? Magnesium may help. Are plants growing only slowly, and nitrates
are at zero? Add that KNO3 and watch the bubbling begin as plants kick into high gear.
THIS STUFF ISN'T SO GREAT - MY PLANTS STILL AREN'T GROWING Are you sure you've supplied everything? Is lighting sufficiently intense for your plant choices,
of good spectrum for plants, and for a long enough photoperiod? Are you giving root plants
such as swords and crypts and aponogetons some root fertilization? If your light levels are
at 2 wpg or greater, are you supplying CO2?
HEY, MY TANK LOOKS LIKE A BUBBLING CHAMPAGNE GLASS! Cool! You did it. You gave your plants everything they need to make their growth lush and green. Now you will require just one more item: pruning scissors!
Written by Cathy Hartland