Hi Tom,

Thanks for the very informative post. Also, thanks everyone else for the
info you have provided.

Over the last 4 days I've introduced some CO2 injection into the tank using
the old 2 litre coke bottle, sugar and yeast mix to generate CO2, and
disolving it into the water using a home built contraption that is
constructed from an old aquarium vaccum cleaner tube fed from the output of
a powerhead with an airstone inside :-)

pH changes were very slow, but at this point I've increased kH from around
1.5 to 4.0 (by addition of baking soda in small steps) in order to maintain
pH 7.0. I've noticed one teaspoon of baking soda increases kH by 1 deg in
my 55 gal tank. pH is currently 7.0 which I believe is around 12ppm CO2 .
Tomorrow I'm expecting a CO2 test kit which will hopefully confirm that
calculation. In any case the fish are all happy and some plants are now
sending strings of bubbles and are showing some new growth.

I believe I understand now the reason why I was able to have a kH reading of
5 deg with a pH of 7.0 without CO2 injection before I moved house. The old
tank was very old, and had been at some time or another either acid or
alkaline so in each case I either added pH-UP or pH-DOWN. After a lot of
reading over the last few days, it seems to me that if one adds a strong
Carbonate buffer (such as pH up) and then adds a strong Phosphate buffer (pH
down), the two will reach an equilibrium in terms of pH, whilst still
maintaining some buffering capacity. Over a period of years this could add
up to a lot of buffering, which is probably what I was seeing with my kH 5
pH 7 reading. Obviously some of each would be lost during water changes,
but the equilibrium would be maintained until such time as the tank crashed
out.

That's my theory, and I'd appreciate any comments.

Regards
Graham.




" wrote in message
om...
"Graham Broadbridge" graham at peachy dot org wrote in message
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I'm no chemist, which is why I posted all the relevant water chemistry.

Regards
Graham

Think of it like a balance, see saw etc. The CO2 is the acid and the
HCO3(KH) is the base. The pH is a ratio of both of these.
The CO2 is a gas and has an atmospheric component. The KH(HCO3) does
not. Therefore the CO2 can leak(be driven off if in excess) out or
leak into the tank(If the CO2 level is understaturated or you add CO2
to enrich your tank). The KH stays the same pretty much unless you
have a relatively few number of plants that can rip the CO2 out of
HCO3= CO2+OH.

You can get confused by the chemistry and theory or you can just
follwo the pH/KH/CO2 table.

Step one:
Measure KH, make sure it's around 3 degrees(~50ppm) or higher.

Step two:

Find the KH you measured and then find the right pH range for a CO2
level of 20-30ppm range on the pH/KH/CO2 chart

Step three add enough CO2 gas ONLY to achieve this pH.

That's it. Try and maintain the pH in that range while the lights are
on.

Maybe someone can explain how I can increase the kH without the pH going
through the roof and killing all the fish. I'm acceptable to all
suggestions.

Well fish live in nature seem to do fine with good sized swings in
areas with high plant denisities. They are not sudden and take most of
the day to slowly ebb and flow diurnally. Most productive systems do
this, some up to 2 full pH units and some shallow lakes with lots of
plants will go from pH 6 to a pH of 10 daily.

But keeping a certain pH locked in is just to supply the right amount
of CO2 for the plants. This is the name of the game, we don't add CO2
to adjust the pH, just supply the plants with CO2. Some seem to think
plants like a certain pH or KH, which is generally not true. All the
plants want is CO2/nutrients etc.

Regards,
Tom Barr