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Re: Terminology, Nutrition
Growth is a technical term which refers to the rate at which plants
increase their biomass. It is generally reported as grams produced per
gram extant per day. A constant growth rate will therefore produce an
exponential increase in biomass over time. An optimal or maximal growth
rate is the maximum intrinsic growth rate of a given plant. Generally,
for fast growing submerged plants this is a doubling time of 1 to 4 days.
This means that if your tank is 1/4 full of plants it will be completely
full in 2 to 8 days. If you then remove 3/4 of those plants, your tank
will again be completely full in another 2 to 8 days... and so on.
With this as a benchmark, it is clear that NO ONE on this list has plants
which exhibit 'good growth'. What successful aquarists have are stable
tanks with a high 'standing crop' of healthy populations of plants. Of
course, few would want to have to deal with optimal growth rates!
Optimal growth rates require at least 20% full sunlight (400 umol/m2/sec
PAR or 2 klux), moderate to rapid water movement, about 20 ppm CO2 in an
acidic or neutral tank or a pH of around 8 to 8.5 (which will deliver
about 45 ppm CO2 as bicarbonate), an adequate replacement rate for
mineral nutrients (either through fertilization or a flow through
system) and a FERTILE SILT LOAM SUBSTRATE.
There is no way that infertile clay substrates can support optimal growth
rates. This has been proven many times over the past 100 years using a
wide variety of substrates and a wide variety of aquatic plants.
Having said that, the use of laterite (which is a highly weathered clay SOIL
found in hot, humid climates that contains large amounts of iron and
aluminum hydroxide and little organic matter) is an effective and SAFE
way to produce stable tanks with healthy plants and a high 'standing crop'.
If you want to be SAFE, then use a laterite soil. Dont fool yourself into
thinking that your growth rates will be high. If you like to experiment,
then get a shovel and find your own mix... you may experience disaster,
and you may find that your plants have taken over your room during the day.
There is generally a threshold concentration below which nutrient uptake
will be reduced and be insufficient for the needs of the plant. You need
a concentration in the tank for a given nutrient that will supply the
plants requirements without falling over time. For Calcium there is also
a water column requirement apart from that amount needed within the
plant. This is because Ca is crucial in maintaining membrane integrity
and cell wall structure, both of which are apoplastic (outside the cell