[cprash]

I need to get my ph down to 6.5 - 6.7 for the livestock I keep. I do however, want to keep the kh between 3 - 6. Is there anyway to achieve this balance?

I inject co2, my tap water is soft but neutral. There is a bag of crushed coral in the filter. I have both Seachem Buffers which can get me to the ph I want, but technically not the kh, since the Acid Buffer turns kH into Co2.

 

[Darkblade48]

I wouldn't worry about your pH; rather than trying to get it into the "optimal" range for your livestock, a steady pH is much more important, in general.

 

[DarkCobra]

Darkblade is right, but your desired parameters are totally achievable.

With a kH of 4 (the majority from carbonates), and 30ppm CO2, your pH will fall neatly into line at 6.6.

Note that a kH test kit will read artificially low on water with CO2 in it, because it measures kH only indirectly, by reading pH. CO2 has no actual effect on kH.

 

[cprash]

Darkblade is right, but your desired parameters are totally achievable.

With a kH of 4 (the majority from carbonates), and 30ppm CO2, your pH will fall neatly into line at 6.6.

Note that a kH test kit will read artificially low on water with CO2 in it, because it measures kH only indirectly, by reading pH. CO2 has no actual effect on kH.

Thanks, i didn't know that.

I'm targeting 4dkh to avoid unpredictable ph swings, mostly as my water is very unbuffered.

To get down to 6.6 (from ~7.2) should I use the buffer combination (1 parts Acid, 1.3 parts Alkaline) or should I target a higher ph and let the co2 do the rest of the work?

 

[DarkCobra]

Don't use acid buffers, it's ultimately futile for the reason you stated in your original post. Alkaline buffers and crushed coral for increasing kH are fine. Let the CO2 do all the work of shifting pH down.

And if by some quirk of water chemistry (rare but possible), the proper amount of CO2 fails to achieve the desired reduction in pH, refer to Darkblade's comment.

 

[wkndracer]

Angelfish as the primary species here in all my tanks. All tanks are planted. Stable TDS is my benchmark once the mineral content is added back not pH readings.

That said, (wish I had your source soft water)
Tanking with 100% RO water, mineral content set with GLA booster and A&H baking soda for several years.
3-5dGH range set by the booster and 2dKH set with NaHCO3.
pH on injected tanks maintained at 6.0 with zero stability problems.

NaHCO3 (A&H baking soda) is routinely used in University of Florida labs to create stabilized KH buffer solutions. It's not a 'temporary' buffer as has been reported in several posts.

Alkaline buffer is also made with a sodium bicarbonate base.