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PMDD, Calcium and the FAQ
The questions about PMDD have occurred so regularly that I believe that its
time that we created an entry in the FAQ for it. I also believe that it
has been in use for long enough that its usefulness seems to be established.
Personally I would like to see the formula updated to include an
optional calcium supplement. I'm not certain that we could get
enough CaCO3 to dissolve but let us pose this question to our
chemists. Do you believe that it's necessary to prepare a separate
Ca(X?) solution? Is PMDD too concentrated to contain enough
Ca? What dose would be appropriate (relative to the other
nutrients)? George Booth supplied the following table:
The following table is based on data from the Feb, 1988 "Today's
Aquarium, the International Magazine of the Optimum Aquarium",
("Aquarium Heute" in German), published by Aquadocumenta Verlag GmbH.
Average nutrient content of plants and aquarium water
+-----------------------------------------------------------------+
| Symbol Nutrient Plant Water Absorbed as Concen|
| mg/kg mg/l Factor|
+-----------------------------------------------------------------+
| O Oxygen 48,000 880,000 H2O 0.02 |
| Abundantly available in the water |
| |
| C Carbon 36,000 Varies CO2(HCO3-) 1000 |
| Absent if CO2 injection is not used |
| |
| H Hydrogen 6,000 110,000 H2O 0.02 |
| Abundantly available in the water |
| |
| K Potassium 3,600 5 K+ 1000 |
| Maybe sufficient with good feeding otherwise fertilization |
| |
| N Nitrogen 3,200 5 NH4+/NO3- 1000 |
| Too much nitrate if overfeeding fish |
| |
| S Sulphur 660 15 SO4-- 50 |
| Fish food and tap water |
| |
| Ca Calcium 650 90 Ca++ 10 |
| Absent in soft water |
| |
| P Phosphorus 460 0.1 HPO4--/H2PO4- 1000 |
| Too many phosphates if overfeeding fish |
| |
| Mg Magnesium 210 18 Mg++ 10 |
| Absent in soft water |
| |
| Fe Iron 15 0 Fe++ 1000 |
| Absent under good light, unless fertilized |
| |
| Other Trace elements 10 0 Ions 1000 |
| Maybe sufficient with good feeding otherwise fertilization |
+-----------------------------------------------------------------+
Notes:
"mg/kg" and "mg/l" are roughly parts per million or "ppm"
"Absorbed as" is the chemical form the plants can most easily use.
"Concen Factor" is how much plants can store beyond their needs for
growth, i.e., plants can store 1000 times more iron than they need.
From this the ratio of Ca to N in plant tissue is 5 to 1 by weight.
If your tap water is hard, then we probably wouldn't need to add
any Ca at all. OTOH, a tank with strong lighting and CO2 can
really suck up nutrients and Ca can often be in critical demand.
Steve