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Re: Hard water

> Our community sits on top of a slab of dolomite. Water hardness is
> about 300ppm  and the alkalinity, about 300ppm with a reading of
> about pH 8.3. I've been cutting with RO water to achieve KH 9. Adding
> CO2 results in lowering the pH, and I can use the charts to determine
> the CO2 content in the water, the target being around 15mg/L.

What's your tap's KH? You will shoot for a pH of about 7.0 to 7.2 with what
you got.
> Question: If I use straight tap water, add CO2 and measure the water
> via Hach titration method to identify the goal point of CO2 15mg/L -
> 30mg/L, I may still have a rather high pH. Am guessing here.  In this
> situation, is high pH a problem for tropical aquarium plants?

No, CO2 is. I suppose one could add 30+ GH/KH to see but why and who has
that kind of water? Growing plants in Mono lake (pH 10.1)?
Well even at a KH of 15 or so it will not be that much higher.
Higher GH's will likely cause more grief than KH's. My GH is 24 no problems
though except fantastic crypt growth etc. I would assume that high Ca not
high HCO3/CO3 would cause the problem, but in both cases I have not seen any
evidences of this. Those who say they do, have other issues(CO2, nutrient
etc). Gloss, hair grass and many other so oft called soft water plants are
teeming and doing well in my liquid rock.
> A colleague mentioned, the possibility of changes in the mobility or
> availability of various ions starts, as pH changes. "For example, at
> very low and (I believe) at very high pH, P may start precipitating -
> with Fe under acid conditions, with CaCO3 under alkaline conditions.
> And the invisible but extremely important nitrifying and denitrifying
> bacteria may be affected."

Not that I've seen from a practical standpoint. Theory yes, but what we are
dealing with here, no. I think the whole RO thing is all a bunch of rubbish
to get folks to spend more $ on RO's instead of CO2 systems. Most, not all,
LFS know little of CO2 set ups(but more are seeing the light and selling the
salt Ca/kalk dissolvers etc so they have CO2 but for SW more than the FW
plant thing). They are getting more into it as we go out and bug/ask/show
Adding CO2 messes with some folks still and if they don't know much about it
they stay away from it.

But if you got plants, add CO2. That's all they are after for the most part.
As far as any problems with high Mg or Ca, I have not seen any, as far as KH
goes, CO3, CO2 and HCO3 are all that's about. As the pH shifts from one end
to the other these species of carbon shift. Higher pH's more CO3, lower pH's
more CO2 gas, stuff in the middle, mainly HCO3. Adding CO2 lowers the pH and
shifts this so called Bjerrum plot to favor high CO2 gas contents. But if
you stop adding CO2 it will equilibrate to the high pH.  Can't remove that
HCO3 and CO3. Well unless you add a strong acid etc but let's not get into
that one.
One thing you might note that is in harder waters you'll need more traces
and macro's to get the same affect on the plants. This doesn't affect
presence of algae from what I've seen. I can get the same algae someone with
soft water can. But I have to maintain higher levels of nutrients in my
tanks than what many that have very soft waters(KH-2 to 4) do. I've done
plenty of work on soft water tanks overtime while having my hard and
moderate hard waters at home with and without lots of P.
The best pH pretty much for nutrients for plants sits around 5.5-6.0 or so.
Not good for us generally or fish or the plants or the bacteria. for the
roots it's good but this idea does not consider all of the plant being
underwater etc. The pH ranges you'll have after adding CO2 will do nothing
to the bacteria's health.
Tom Barr  

> John Glaeser