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.

In the future, I probably will only use RO water to keep the nitrate (which
is 15 mg/l in the tap water) and the KH which is 15 and all the other stuff 
like pesticides out of the tank.


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...)

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.

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.
I am asking because I see these little holes in my plants' leaves (especially
in the Hygrophilia stricta). I read that it may be an Mg defficiency, therefore
I started to add Duplagan. Now I have the full set: Duplarit-K in the ground
and Duplaplant, Dupla-24 and Duplagan in the water (but still no heating
coils in the ground). No, these are no snail bites, they look different.
I also have them :-) 

I still wonder if there may be other defficiencies because of the RO water.

Some plants (especially the rotalas) still lose 1 or 2 lower leaves every day. 
But maybe they are planted too close so that the lower leaves don't get 
enough light, I am not too sure about that. I have 30 watts + reflectors for
the 27 gallon tank.

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.

Thanks a lot to everybody, also for the last responses & mails on algae
fighting. Andi from Munich, Germany.