newbie question: why is high ph and hardness bad for plants?

plantbrain said:
Dropping your pH without CO2 will not help the plants, they will grow better without injection in HARDER KH's............actually.........

Since KH(more specifically HCO3) can be used as an alternative to CO2.
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so just leave my tank as is?

also how much fertilizer should i add? From what you have told me i have come to believe that it is my low light (1watt/gal) and possibly low CO2 levels that are the limiting factor to plant growth

This assumes that the plant can/will use HCO3...

...So Vals, Hydrilla, Egeria, pondweeds, most all algae can.
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java moss is a pond weed, right? is there like a comprehensive list i could look up to see what plants i can use?
 
Good stuff and explains why with my ultra high GH (800 PPM) and my high PH (9 PPM) I have never been able to have any aquatic plant plant out grow the rate at which it dies off and also explains why my terrestrial plants in contrast do so very well becasue only their roots are exposed pulling nutrients while the rest of the plant is out side the water getting all the highly available CO2 it needs from the air and unfiltered-unrefracted low power light. So for my water conditions I think aquatic plants are out of the question unless I want to fight an uphill battle something I have tried ans failed as you just cant fight calcium & magnesium in such high levels no matter how much acid you use, and RO is a balancing act not unlike juggling glass bulbs you end up having crashes.

For me and probubly anyone else that has very hard water, terrestrial low-light plants grown hydroponically is the way to go.
 
hmm so if i get this right carbonate or C0 subscript 3, superscript -2. Is the ionic salt to carbonic acid HCO subscript 3, superscript -1. Normally will not will not exist in low ph environments because it is tied up the the proton in carbonic acid, because carbonic acid has a low Ka and therfore will only dissociate in a low proton environment.

and a low proton environment is high ph water, so then it dissociates, leaving hte carbonate ion free to get picked up by plants that can utilize it...yes?
 
so the solution is to buy hardwater plants?
 
so i just got out of my environmental science class and learned this today

CO2 becomes CO3 and 2H+ at kh ~ > 20mg/L

so the extra H+ make the ph go up... which is why ph is a sign that kh could be high but not the reason why.

so im thinking that adding CO2 will just make for more CO3 and H+ and bring the pH even higher, is this correct?


so what I need to do is lower my Kh which is high due to two possible sources
-local tap water (ph 7.8 which could mean high kH)
-pea gravel substrate from home depot
and i need a kh testing kit

so the possible solution would be to get water from a different from a different source and/or change my substrate.


i just asked someone "does san jose have hard water"
"ya we got some of the hardest"
 
no free floating H+ is what brings ph down. These H+ ions get picked up by water h20, to from h30+ (hydronium)

a high ph soulution is low in H+ and is abundant in OH- (hydroxide)
 
All this chem is fine and dandy, till.........you start enriching with CO2 gas.

This throws those equilibrium off a fair amount.
You can use the pH/KH chart to measure CO2............but this assuems there are no other acids and that all the alkalinity is bicarbonate.

This can be very different depending on the tap water.

Some are fine, others supposedly have 220 ppm of CO2, and the fish and plants are fine etc.

There are ways around these issues, but they have trade offs and can be troublesome.

All in all, measuring CO2 accurately in a planted tank is the hardest by far........of any analysis or test to do and confirm/calibrate.

Keep this in mind when you measure and test, do not assume, confirm.
We can do this using a reference solution for NO3, PO3, even pH.....temp etc etc...........

But CO2 is much more problematic.

Regards,
Tom Barr
 
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