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[APD] Re: clay balls or jelly balls

Daniel Larsson wrote:
> Steve Pushak asked:
> >Using agar to slowly diffuse nutrients is an intriguing idea but why
> bother?
> Because you can remove it and it doesn't make dust-clouds when
> rearranging plants, which I do every week.

I never need to remove a clay fertilizer ball. It's not organic and thus
won't decompose. It continues to make nutrients available to a plant for
months. If I were to rearrange Crypts, Anubias or Echinodorus by uprooting
them, then I would be asking for trouble. It's better to put these plants
into a pot with soil if you think you might want to rearrange them or if you
need to remove them for harvesting purposes. These are the types of plants
which I might typically want to fertilize at the substrate.

For fast growing stem plants, You can probably uproot them without harming
them significantly but then you don't really need to have any substrate
fertilization to get what you want. Its easier to chop these guys off at the
root level, discard unsightly portions of the stems & replant the tops.

Clay balls have never caused a problem of dust-clouds in the water. Perhaps
you are thinking of a substrate that uses soil or clay throughout the
substrate. That is not necessarily the case with clay balls and certainly,
the clay ball will not be releasing a cloud of dusty water. In fact, you can
remove one with little trouble at all, if you needed to.

> So the prospect of nice removable jelly balls not making a mess
> is awesome, but I still need feedback on how strong one would
> make them.

You can estimate the amount of each nutrient that you need by estimating
your daily consumption and the number of days that you intend the nutrients
to last. Hopefully, you will come up with the desired number of milligrams
of fertilizer that you need.

In practice, the diffusion rate will depend upon the geometry of the ball &
concentration gradients within the jelly and so the release rate will decay
asymptotically. Its a tough problem to solve theoretically.

Experimentally, you can determine the maximum, initial release rate by
preparing a known arbitrary concentration of agar jelly & place it into a
jar of water of known volume. Divide the measured concentration in the jar
after one day by the ratio of jar to tank volumes and you will get the
expected concentration in the tank from that agar ball. If the result is 0.1
ppm N and you desire 1 ppm N after 1 day, then increase the nutrient load in
the ball by a factor of ten. Can your plants keep up with a daily addition
of 1 ppm N? That would seem to be a upper estimate, however 0.1 ppm might be
more practical.

new subject: "Nitrogen consumption rate"

To ask this question another way, how many milligrams of N are people dosing
using the PMDD regime and at what frequency? Other pertinent data needed
are: tank volume, CO2 injection rate, lighting level & type of plants grown

In practice, I add a pinch (50 to 100 mg of K2NO3) to a 20 gal about once a
week until things start to get out of hand. That's equivalent to 5-10 mg N /
80 L = 0.06 - 0.12 mg/L weekly. That's a well lit, CO2 fertilized tank of C
pontederiifolia, 1 A madagascariensis, 1 large Alternanthera, 5 or so
Lobelia cardinalis & 1 medium Anubias lanceolata. Mainly a slow growth tank
but I need to perk up the lace plant. I can't keep that up indefinitely as
things start to get out of hand after a few weeks. Either the tank is full
of plants or hair algae.

Steve P

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