Re: APD V2 #126 Response to RO questions

>From: hermel at ibm_de
>Date: Thu, 8 Aug 1996 14:08:25 +0200 (DFT)
>Subject: RO water + minerals
>Hi everybody,
>some questions on RO water. I plan to buy an RO unit but already now, I am
>mostly using RO water for water changes. Mostly means: Changing 30 liters,
>I use 25 liters RO water and 5 liters of tap water.
>1) As RO water contains almost no minerals, is it enough to add Duplaplant
>   tablets and daily Dupla-24 and Duplagan during the water changes? Or am
>   I still missing important minerals (or other stuff) for the plants and
>   the fish?
>2) As long as I add some tap water, could that be the source for missing
>   elements? How much tap water would I need for it? (Although I don't want
>   to use tap water really...)

As long as you are using 20% tapwater AND the Dupla, I believe you are
getting enough trace elements into your water.

>3) At the moment my KH is 4 and the GH is 8 in the tank (because I was a
>   dummy, I started with pure tap water and reduced the hardness over time
>   with RO water in the tank). I guess that when KH is below 3, I will use
>   KH+ or whatever it's called after water changes to raise it again.
>   What level of KH should I aim for? I use PH-controlled CO2 injection,
>   PH is 6.8, CO2 is 20 mg/l.

Most aquatic plant books recommend a minimum KH of 3, although some plants
can handle down to KH2. Note that sub-adult fish may also require a KH of 3
or more for growth.

>4) Do I have to raise the GH also? Or does it increase with the KH? If not,
>   what level is appropriate? My fish are mostly red and diamond neon tetras
>   (and some algae eaters like SAEs and ancistrus + corys), plants are anubia,
>   cryptocoryne, hygrophilia, limnophilia, vallesneria, rotala.

GH and KH are technically independent variables. Testing for KH is very
specific in that it measures Carbonates. GH is a non-specific test for a
value that has been evolved in tradition. It is a gross indicator of
"everything except water" in the sample. (Same for conductivity). For
example, a high GH could be caused by either calcium, iron, magnesium
etcetra, or any combination. In general, I try to keep my planted discus
tank at GH of 4-8 degrees.

>Fe is 0.7 mg/l although I use 150% of the recommended dose of Dupla-24
>I wonder if the test kit maybe does not register chelated Fe? It's a JBL
>Fe test kit, probably not available in the US.

In my experience, I have found that it is very hard to keep the iron level
up in a growing planted tank. I don't know what type of iron your kit
measures, but chelated iron is what you need.

If I get any "color" at all from my iron test kit, I consider that
acceptable. I believe that you can have problems (and problems similar to
yours), by iron overfertilization.

I have also run into difficulties trying to bring down KH & GH by adding
pure RO/DI water over time. I did not monitor KH closely enough and when
the plants started rapid growth, the KH dropped drastically, as did iron.
Leaves started dropping, nitrates shot up .... ugly.

In short, I recommend careful observation when changing RO/DI water mixes,
and when adding trace elements.

> Andi from Munich, Germany.

-Bill Brady  Harwood, Maryland USA