Tom, seems I remember you saying there was an ideal GH of 3, a KH of 5. I know that plants can thrive within a wide variance, but is there an ideal GH and KH, and perhaps a Ph, that in general, is more beneficial for plant growth? :gw

More likely I said a GH of 5 and KH of 3.
GH should always be higher than KH if you have a choice.

I think pH has little relative importance wereas total GH/KH and CO2 do.

Regards,
Tom Barr

High pH reduces the amount of CO2 that water can hold. Above 8.0 it greatly reduces the kinds of plants that can be maintained.

This is very significant in non-injected tanks.

Bill

So why do high pH conditions cause plants to grow better if you do not inject CO2?

Here's a hint:

Does hard water have the same or less CO2 than soft water(two glasses sitting on the table full of water, no added CO2)?

Next question, can plants use HCO3-, the bicarbonate ion? Now which glass of water has more HCO3-?

Now add those two together for your answer.
Which has more carbon(the sum of CO2 and HCO3) for the plant under these non CO2 conditions?

Regards,
Tom Barr

Tom,

To answer the first question, if by "hard water" you mean the disolved calcium and magnesium cations (aka GH), I would expect the amount of CO2 to be the same in each glass.

The carbonate anions (aka KH) are better referred to as alkalinity, not hardness. But you know all that stuff.

Given that, the second question doesn't seem to be related to the first, but a few plants can use KH directly (but I think they'd rather not, given their druthers.)

So, to rephrase my question, if there was one glass on a table that contained water with a pH of 8.0 (and a GH of whatever), wouldn't it would contain relatively little CO2?

If another glass contained water with a pH of 8.0, a GH of whatever, and a KH of 10, a chart at The Krib shows that it would contain 3 mg/liter of CO2. http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html

So I would surmise that only a small number of plants could be cultured at such a high pH, those few that could use the KH as a carbon source, such as vallisneria, sagittaria, elodea, and ceratophyllum. Right?

Thanks for the continuing turoring!

Bill

No,why would it?
It would have the exact same CO2 ppm as the glass with a pH of 7.


No, there are many many plants that use bicarb. Myrio's, Swords, Egeria, Hydrilla, all pondweeds, vals, sag's that's not a few..........

The pH is not the issue, the CO2 and availability of alternate sources of carbon should that become low is.

From the pH/KH table=>

pH 7 and a KH of 1=> 3ppm CO2
pH 8 and a KH of 10 => 3ppm of CO2

They have the same CO2 and both are at about ambient levels.
Which has more *total* carbon?

The one with the higher pH.........now why?

Regards,
Tom Barr

That's not a few, I agree, but as a percentage of all aquarium plants? Maybe 5% (to pick a number) can use bicarb directly AND thrive?

I think the consensus is that crypts in general, for example, cannot use bicarb. But I've also read postings from people who say that they have done this, so . . . ?



Yes, I see that, but if the carbon in the bicarb is not useable by the plants that one is trying to grow, of what use is it?

Maybe a better question is, "What plants cannot grow in a high pH/low CO2 environment, without special measures like very high levels of lighting and ferts?"

Bill

But the trade off for Crypts: they has low CO2 demand since they grow slow.
But.....Crypt affinis does extremely well in hard water, so does C aponogetifolia among other hard water crypts.
So this is not really true either.

A plant such as Isoetes uses CO2 at night, some use C4 metabolism, some use direct bicarb use, some indirect.


It's of no use if the plant cannot use it, but most can/do.
Few people have tanks without a plant species that doesn't use bicarb....so you will see some plants thrive when the CO2 drops and some that are pretty sensitive.
If the CO2 issue gets worse, the algae will apear and bloom also.

Tonia does not appear to be one, L cuba does poorly without good CO2, picky plants in general.....tougher hardy plants, the so called true aquatic you find in most systems in nature and permently submersed over several years, these tend to be the ones that have adapted to the low CO2 levels by using bicarb.......

The less adapted aquatics, sometimes they are marginals, amphibous, creeping surface(so they still use the air CO2), some are often not even found near water in nature(some Ammannia etc) often will be the ones that don't have the bicarb use ability.

But the pH thing, it's mainly an issue of CO2, not the specific KH/pH.

Regards,
Tom Barr