Re: Duplaplant + KNO3?

> From: hermel at ibm_de

> Q1: I am using the Dupla system. Are there any of you who add KNO3 in
>     to the Dupla fertilizers to prevent nitrate limitation? Is this a 
>     recommended method? Experiences?

I use KNO3 in addition to Dupla24. (I don't use any other Dupla fertilizers
in this sand-over-humus substrate tank.) This has worked tremendously well
in promoting growth in a nitrogen-limited situation with fast-growing
plants. It has allowed them to outcompete the cyanobacteria which had been
hassling me until then. I fertilize to about 3-5ppm NO3.

I can't answer your second question (what happens to the extra K+ ions). My
guess is that it builds up and is removed with water changes. Someone
posted to this list a very cool quantitative summarization of how high
concentrations reach in these situations, using a summed series. It's
fairly intuitive - fewer larger water changes reduce ion buildup
drastically better than more frequent smaller water changes.

> Q3: For a 200 l tank to achieve a nitrate level of 5 mg/l should I simply
>     5 * 200 = 1000 mg = 1g of KNO3?

Almost. The molecular weight of KNO3 is 101. The molecular weight of the
NO3- ion is 62. So every gram of KNO3 adds about .62g of NO3 (and about
.39g of K+). This means that for every gram of NO3 you want to add, you
should add 1/.6 or about 1.67g of KNO3.

You will find that accurately measuring gram amounts of powder like this is
hard. Scales with sufficient precision and accuracy are available (they are
used for reloading ammunition); they run about $45 mail order.

In any case I recommend highly that you underdose the first few days with
the KNO3 solution, and measure nitrates daily to see how much of the
nitrate your aquarium is metabolizing. I made up a liter of solution for my
aquarium, which I had mixed for convenience so that 10mL of the solution
would raise the nitrate concentration in the aquarium by 1ppm.
Unfortunately I made a mistake and actually mixed it so that 10mL of the
solution would raise the nitrate-nitrogen concentration by 1ppm, off by a
factor of 4.4. I noticed this when I tested nitrate an hour after
fertilization, and instead of the expected 4ppm, I had about 20ppm!

  moving aquariums this weekend to a new neighborhood in Seattle