"blank" wrote in message
...
My tank is 75gal low light, medium stocked community freshwater with at
least 1/3 plant cover, no CO2. For the past couple of weeks I've been
adding Flourish, Trace and Nitrogen at the recommended rates, and do a 50%
water change weekly. The plants have improved in colour and growth very
noticeably.

Tank water: pH 7.8, GH 6, KH 5, Nitrate 5, Phosphate 0.75 (Tap water is
8.4, 3, 3, 0.25)

I've finally begun to try to raise the KH in an attempt at increasing the
CO2 level, so added 3 tsp baking soda, which produced little change, then
added the recommended additonal 3 tsp today, which brought the KH up to 8
and didn't affect the pH. So far so good.

Looking at the standard CO2/KH/pH table, it seems I need to increase the
KH
to about 20 to even get close to the optimal CO2 level. Which means I'm
going to be adding a lot of baking soda each week. My plan is to add 6
tsp
daily, monitor KH & pH, until I get up toward a KH of 20, and then, once I
know how much to add, add the appropriate amount with my weekly water
change
in order to maintain the high KH. Does this sound like the right
approach,
or am I about to create another disaster?


Increasing the Kh will not increase your CO2 level....only adding CO2 does
that (!)

Increasing KH without altering CO2 will increase your Ph so I'm not quite
sure how you managed to add Baking soda & not affect Ph....it doesn't
compute - suggest you test it again. Quite often you will see tap water
having a lower than expected Ph level - this is because it sometimes
(usually) contains artificially high levels of CO2 when it comes out the
tap. Water that has just been filtered through peat does the same thing
(only to a much greater extent). In both cases the excess CO2 will escape
over a matter of hours & the thing will settle back to the standard 2-3ppm.

You seem to have understood that there is a relationship between KH, Ph &
CO2 but just perhaps not how it works. The two variables are Kh & CO2. The
Ph is the product. Altering one of the variables (CO2 or Kh) will alter the
product (Ph) but it won't affect the other variable. So adding Kh won't
change your CO2 level & playing with CO2 levels won't affect your - Kh but
altering either one will affect the Ph.

Short answer, in order to increase CO2 you need to add it one way or
another.

HTH

Iain

rgds

I.