RO water + minerals

From: hermel at ibm_de
Date: Thu, 8 Aug 1996 14:08:25 +0200 (DFT)

> 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?

You still need to adjust KH and GH to suit the environment you desire.
Duplagan has some calcium and magnesium (for GH) but you probably will
want to add more of each.  A ratio of 2:1 Ca/Mg seems to be indicated
in "The Optimum Aquarium".  The actual GH will be dictated by the
plants and fish you keep.

> 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...)

Except for Ca and Mg, I think the Dupla products and fish food will
supply all the trace elements you need.

> 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.

A KH of just over 4 degrees is called for to achieve the pH/CO2 you

> 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.

You can raise KH by adding baking soda (sodium bicarbonate) or you can
raise KH and GH by adding calcium carbonate.  A GH of 5 degrees would be 
good for a community tank. 

One teaspoon (about 6 grams) of sodium bicarbonate (NaHCO3) per 50
liters of water will increase KH by 4 degrees and will not increase
general hardness.  Two teaspoons (about 4 grams) of calcium carbonate
(CaCO3) per 50 liters of water will increase both KH and GH by 4
degrees.  Different proportions of each can be used to get the correct
KH/GH balance dictated by the fish and plants in the tank.  Since it
is difficult to accurately measure small quantities of dry chemicals
at home, a test kit should be used to verify the actual KH and GH that
is achieved.

> Fe is 0.7 mg/l although I use 150% of the recommended dose of Dupla-24
> everyday.  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.

A level of 0.1 to 0.15 mg/l is sufficient.  I would recommend reducing
the amount of Dupla-24 you use.  Perhaps the higher iron levels are
blocking the uptake of other trace elements.