GH and plant growth

[rich_dog_22]

I am thinking of starting up my first planted tank and I have really hard water...something around 17 degrees....i was wondering what kind of limitations on which types of plants one can grow under such hard conditions

I know there are enough of you out there with really hard water and am wondering if there are plants that are a good idea to stay away from if you are not willing to fork out the money for RO or dont want to make the frequent trips to the water machine at the supermarkets for water changes

rich_dog_22

[plantbrain]

As long as the GH is above 3, you are fine. Mine was 25GH. Plant do fine as long as there's enough. GH is Ca and Mg both of which are major plant nutrients.
This is an old myth that seems to go on and on and never gets killed off completely.

Regards,
Tom Barr

[wetmanNY]

Which myth is being referred to here? There are so many...

[plantbrain]

Hummm.........I posted an answer yesterday now it's gone.

The myth that claims high GH is bad for plants, GH 3 or 50ppm or higher is good.
Regards,
Tom Barr

[Starry]

Tom: What about the KH?

Last summer my plants were growing like mad. 2.6wpg PC on a 10gal with DIY CO2. KH 3-4, pH around 7. Plants loved it. Then I moved to university for 4 months. KH around 12 or so, pH high. I can look up the exact numbers if you want. That's when things started going bad. Barclaya rotted. C. balansae loved it, but not much else. Limnophila refused to grow. Sagittaria got choked in algae and stopped putting out runners. Mayaca got algae AND didn't grow. Alternanathera looked pathetic. A. ulvaceus went dormant and hasn't come back. And I had DIY Co2 as well. Water changes always the same - weekly 10-30%. Now, I've been back for 2 months and things are looking up (except the poor Braclaya).

Any comments? Suggestions?

[plantbrain]

KH is a measure of HCO3 for our purposes.
www.sfbaaps.com under "ref's" you'll find a table with pH and KH on the axes and CO2 levels in the table.

If you have a KH of 4, you should try for a pH of 6.6 for 30ppm.
If you have a KH of 12, a pH of 6.9 to 7.0 is good and will give close to the same CO2 level.

So you add enough CO2 gas to get these pH's.
That's it.

All the KH is about really is to measure the CO2. Plants want CO2, not a specific GH or KH except above 3. There's two part to CO2 measurement, not just pH and not just KH but rather both.

Plant "like" low KH's is another myth. Plant "like" CO2.

regards,
Tom Barr

[Starry]

I get what you're saying, that's not something I need to have explained to me. But I never had a pH of 6.6 with a KH of 4. It was more like 7.0-7.2-ish. And, when my KH was much higher, around 10-12, my pH was around 7.4-7.6. Roughly the same concentration of CO2. But BIIIIG difference in plant growth (or lack or growth I should say)


Originally posted by plantbrain
KH is a measure of HCO3 for our purposes.
www.sfbaaps.com under "ref's" you'll find a table with pH and KH on the axes and CO2 levels in the table.

If you have a KH of 4, you should try for a pH of 6.6 for 30ppm.
If you have a KH of 12, a pH of 6.9 to 7.0 is good and will give close to the same CO2 level.

So you add enough CO2 gas to get these pH's.
That's it.

All the KH is about really is to measure the CO2. Plants want CO2, not a specific GH or KH except above 3. There's two part to CO2 measurement, not just pH and not just KH but rather both.

Plant "like" low KH's is another myth. Plant "like" CO2.

regards,
Tom Barr

[plantbrain]

"I get what you're saying, that's not something I need to have explained to me. But I never had a pH of 6.6 with a KH of 4. It was more like 7.0-7.2-ish. And, when my KH was much higher, around 10-12, my pH was around 7.4-7.6. Roughly the same concentration of CO2. But BIIIIG difference in plant growth (or lack or growth I should say)"

It was something else if your testing was correct and if the CO2 levels were maintained at the same level. HCO3/CO2 is nothing but a ratio and pH determine's how much the ratio will be. There's no voodoo in there. It's _all_ about the CO2 level.

I'd look elsewhere if you have growth issues.

I've had no differences in KH's of 10 vs 3 in the tanks and Tap water I've used. Your new tap might not have PO4 etc, DIY CO2 tends to be the weak link. Time when you take you test measurments can play a big role with CO2.
Regards,
Tom Barr