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Old 02-09-2009, 11:38 PM posted to rec.gardens.orchids
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First recorded activity by GardenBanter: Oct 2006
Posts: 11
Default Akerne's RAIN MIX

Hello all,

A lot of discussion has been going on on rec.gardens.orchids lately
concerning our “RAIN MIX” and the amount to use per litre.
I thought the group here would benefit as well from our answer we
typed as a response to some questions received directly.

The recommended dosage for RAIN MIX is as follows:

0,5 g/l = ~ 520 µS/cm = ~ pH 6,1

A little note concerning TDS measurements:

A TDS meter measures the conductivity of a saltsolution and gives,
through a conversionfactor, a reading of the amount of disolved salts
expressed in ppm.

Most TDS meters have a conversionfactor of 0,50 and are therefore
correct for measuring NaCl-saltsolution.
0,01 mole/l solution of NaCl contains 585 mg NaCl/l and gives an EC
value of 1155 µS/cm.
585 mg NaCl/l = 585 ppm TDS
585 / 1155 = 0,506

Unfortunately we are not measuring a saltsolution of NaCl, but a NPK
fertilizer saltsolution. Every salt in that mixture has a different
In a mix of salts one must take into account the contribution of
conductivity of each individual ion and also the interactions between
these ions. Therefore one must use a different conversionfactor for
each different combination.

On regular TDS meters the conversionfactor cannot be adjusted/changed,
on more expensive, professional meters this can however be done.

Put 1000 mg of RAIN MIX in beaker of 1000 ml. Add demineralised water
and shake until all salts are disolved.
Measure the amount of salt with your TDS meter. You would expect to
obtain 1000 ppm TDS, however this is not the case!

For this reason in professional horticulture µS of mS is used and not
Likewise the amount of N is expressed in mmole/l and not ppm.

How much ppm N does a solution contain with 0,5 gr RAIN MIX / liter?

- NPK RAIN MIX = 13-3-15
- amount of N = 13%
- 130 g N per kilo RAIN MIX
- per 0,5 g RAIN MIX you have 130 g / 1000 g * 0,5 g = 0,065 g or 65
mg N present
- this 65 mg N is in 1 l of water = 1000 ml = 1000 gr or 1000000 mg
- 65 mg/ 1000000 mg = 65 ppm N

In order to give you extra information have a look at the following
(source: )

With our recommended dosage (0,5 g/l to obtain a conductivity of 520
µS/cm) we are closer to the 50 ppm N in the below charts to make it
easier for you all.
Our recommended dosage caters for all orchids be they salt sensitive
plants like Disa, Pleurothallids in general over to Paphiopedilums to
the really big eaters like Cattleya and Cymbidium and requires NO
flushing with pure water.
Hence our dosage is a good value for all type of orchids and has been
tested for over 2 years on our orchids (no exclusion) and the mixed
orchid collections of a few selected orchid amateurs!

If you look at the 125 ppm N column than you will see that the
conductivity is 1000 µS/cm… this means you will run into problems with
salt sensitive orchids and you MAY need to flush with pure water every
x time!
A complete waste of fertilizer… and money ;-)

If you cannot see the below charts properly then please visit the page
mentioned above and go the section on the 13-3-15 fertilizer!

EC chart
ppm N 50 100 125 150 200
EC 0.4 0.8 1.0 1.2 1.6

Mixing Instructions
50 ppm N 100 ppm N 125 ppm N 150 ppm N 200 ppm N
Per U.S. gallon of fertilizer 0.05 oz.
(1.4 grams) 0.10 oz.
(2.8 grams) 0.12 oz.
(3.6 grams) 0.15 oz.
(4.3 grams) 0.20 oz.
(5.7 grams)

Mixing Instructions -Imperial Gallon
50 ppm N 100 ppm N 125 ppm N 150 ppm N 200 ppm N
Per Imp. gallon of fertilizer 0.06 oz.
(1.68 grams)
0.12 oz.
(3.36 grams)
0.14 oz.
(4.32 grams)
0.18 oz.
(5.16 grams)
0.24 oz.
(6.9 grams)

kind regards,


Akerne Orchids
Laarsebeekdreef 4, B-2900 Schoten, Belgium
tel. +32 (0)3 651 40 36 fax +32 (0)3 653 06 76

See us at the following shows and events in 2009:

• Gentse Orchideeëndagen, Ghent, Belgium (October 9-11)

Looking for orchid books and magazines? Visit

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