# What's the latest consensus on the effect of high KH on plant growth?



## soham (14 Nov 2017)

Dear members,

What I have read in various forums so far is that high GH values isn't a big deal for most plants and they grow just fine. There seem to be a difference in opinion regarding high KH values. My first question is what's considered as a high KH level? Mine is 9 dH. Is it high or medium? 
Secondly, What's the max KH level upto which most plants do well?
and what's the cause of poor plant growth in very high KH level? I have read it causes impairment of iron absorption. Anything else? 

Thanks,
Soham


----------



## kadoxu (15 Nov 2017)

I think you are a bit confused here... I may be wrong, but I believe it's the other way around. 

High GH (General Hardness) may cause deficiencies if you don't have proper chelators on your fertilizers. My GH is around 13 and all my plants are fine, but I do have to provide Iron with a special chelator.
KH (Alkalinity) is mainly a PH buffer which makes it harder for PH to change rapidly. My KH is usually around 9 and I never had an issue with it.


----------



## dw1305 (15 Nov 2017)

Hi all, 
I think it depends upon the plant. A few plants will only grow in <"very soft water">, but most are fine across a whole range of hardness. 

Some plants (_<"Vallisneria australis"> etc_) have adaptations to allow them to use <"HCO3- as a carbon source"> and they tend to only really do well in harder water. 

The carbonate hardness (dKH) effects the pH, because of the <"CO2 ~ bicarbonate ~ carbonate equilibrium">. 

If you have carbonate buffering the pH of the water will be ~pH7.8, and some ions are less available at pH levels above neutral. Usually dGH and dKH values will be correlated because CaCO3 is, by far, the most likely source of both. 





cheers Darrel


----------



## nel.pogorzelska (15 Nov 2017)

There are some problems with chelators with high pH. High KH is causing high pH. Never heard of GH having anything to do with that actually... High GH means only that you will need to dose more to maintain proper balance (high magnesium and calcium stopping plants from taking other nutritions).
KH on it's own won't cause problems, but pH that probably is high with this KH will. Mostly with iron chelates. I saw somewhere nice charts about chelating ability and pH...


----------



## ceg4048 (15 Nov 2017)

soham said:


> What I have read in various forums so far is that high GH values isn't a big deal for most plants and they grow just fine.


Hello,
        High GH is annoying because it causes calcium deposits  on your kettle and unsightly water spots on tank glass and equipment. However, the consensus is that there is very little impact on the vast majority of plants. The consensus is based on experience as well as on analysis.



soham said:


> My first question is what's considered as a high KH level? Mine is 9 dH. Is it high or medium?


Typically, dKH 0-5 is considered soft, 6-10 is considered medium and 11 and above is considered high.



soham said:


> What's the max KH level upto which most plants do well?


No one, that we know of, has reported having tap water that is so high in alkalinity as to prevent growth and health of the vast majority of plants. There are perhaps a handful of plants that may respond negatively to high alkalinity.



soham said:


> what's the cause of poor plant growth in very high KH level? I have read it causes impairment of iron absorption. Anything else?


The same thing that causes poor plant growth in low, medium and high KH water: poor attention to CO2, flow and distribution and poor maintenance and poor nutrient dosing.

Here is a typical tank with dKH 15+ and GH 25+
If your plants fail in high dKH water then YOU are to blame. Do not blame your water.



 

Cheers,


----------



## soham (15 Nov 2017)

ceg4048 said:


> Here is a typical tank with dKH 15+ and GH 25+
> If your plants fail in high dKH water then YOU are to blame. Do not blame your water.
> 
> 
> ...



Thanks for clearing up the confusion. That's a pretty inspiring tank.


----------



## rebel (15 Nov 2017)

@ceg4048 , very nice high Kh tank! Did you find that you had do anything different with co2? For example inject a little more than the usual amounts for a soft water tank?


----------



## ceg4048 (15 Nov 2017)

rebel said:


> @ceg4048 , very nice high Kh tank! Did you find that you had do anything different with co2? For example inject a little more than the usual amounts for a soft water tank?



Hi,
    No, CO2 does not care about high KH. It dissolves in High KH water exactly the same as in low KH water. I did input high levels of CO2, but that was due to high lighting and high plant mass. The same was true when I used RO water, but collecting and storing RO was more trouble than it was worth, so I abandoned RO and went back to tap.

Cheers,


----------



## rebel (16 Nov 2017)

ceg4048 said:


> Hi,
> No, CO2 does not care about high KH. It dissolves in High KH water exactly the same as in low KH water. I did input high levels of CO2, but that was due to high lighting and high plant mass. The same was true when I used RO water, but collecting and storing RO was more trouble than it was worth, so I abandoned RO and went back to tap.
> 
> Cheers,


Thanks Ceg. Its very interesting to see pogo helferi grown in hard water. Were there any advanced plants that you couldnt grow in this set up? Difficult Erios for example?


----------



## ceg4048 (16 Nov 2017)

rebel said:


> Thanks Ceg. Its very interesting to see pogo helferi grown in hard water. Were there any advanced plants that you couldnt grow in this set up? Difficult Erios for example?


Well I haven't tried all, but I did have a great deal of difficulty with Ludwigia inclinata  "Pantanal" as well as with Tonina.

I wasn't aware that P. helferi is supposed to not do well in hard water. I don't think I've ever grown it in anything else.

A lot of problems that we have with certain plants, and which we blame on hard water or Iron toxicity, or whatever phantom reason, is actually a result of poor CO2 implementation. Not all plants are equally adept at sequestering CO2, so in the same tank, we may see some plants do well while others do poorly. The assumption is then made that because the majority of the plants are doing well, then CO2 for all must be good. Many folks also do not realize that the expression "poor CO2" does not automatically refer only to poor injection rate. It is very possible, and often the case, that poor CO2 occurs alongside high injection rates.

In a CO2 injected tank P. helferi does not appreciate poor implementation of CO2, yet, it can be grown successfully in a non-CO2 enriched tank.
This seeming paradox can only be understood when we understand the basics of how CO2 actually works.

If your helferi is not doing well in a CO2 enriched tank, try supplementing your gas with Excel.
Since it's usually grown as a carpet plant, it typically is placed in the front and is near the substrate, so, like all carpet plants, it's necessary to pay close attention to flow/distribution.

Cheers,


----------



## rebel (13 Apr 2018)

Thanks for this detailed reply. I read it earlier and again today. 





ceg4048 said:


> Well I haven't tried all, but I did have a great deal of difficulty with Ludwigia inclinata  "Pantanal" as well as with Tonina.
> 
> I wasn't aware that P. helferi is supposed to not do well in hard water. I don't think I've ever grown it in anything else.
> 
> ...


----------



## dw1305 (19 Feb 2022)

Hi all,
Edit: Apologies this should have been posted in <"Water parameters & plant help">, thanks to Karl (@Zeus. ) for alerting me and apologies to the OP.

Welcome to UKAPS.


Jan_H said:


> GH has gradually risen and now it stable (GH=KH=16-18). Things have improved. I see better growth of the plants, but I also fight with algae (pretty much all - diatoms, GSA, BBA, BGA).


These are the sort of dGH and dKH levels <"many of us will have"> in our tap water. 


Jan_H said:


> This helps, but the tank is clearly not in equilibrium (it never was). I now focus on optimizing nutrients. NO3 is typically 15-30 mg/l and it comes at this level in the tap water. PO4 and Fe are not measurable. In my opinion, the algae growth comes from too much NO3 and not enough PO4 and Fe. I add these to water column (EasyLife Fosfo and JBL Ferropol). I add 0.2 mg/l pf PO4 once a week and 20 ml of Ferropol (0.1 mg/l of Fe) 4 days after the PO4.


We probably need a photo of the tank to assess plant growth. I'd guess that you are having some nutrient issues, with one, or more, of the <"fourteen essential nutrients"> for plant growth in deficit.

Have a look at <"Frogbit taken a turn"> it shows iron (Fe) deficiency and the recovery from it. I like a floating plant as a <"canary">, because it takes CO2 availability (and light) out of the equation.

Iron is a common deficiency in hard water and it maybe that the JBL Ferropol doesn't supply any iron in a <"plant available form">, @Zeus. will probably be able to supply the answer?

cheers Darrel


----------



## hypnogogia (19 Feb 2022)

Jan_H said:


> I add 0.2 mg/l pf PO4 once a week and 20 ml of Ferropol (0.1 mg/l of Fe) 4 days after the PO4.


I’d suggest that these levels are too low.  Aim for about 0.5ppm for iron and 3ppm for PO4.  Also, given your pH, how is your iron chelated to ensure that it’s accessible to your plants.  Do you happen to know what your potassium and magnesium values are? You can get these from your tap water report.


----------



## Cédric (26 Nov 2022)

ceg4048 said:


> Many folks also do not realize that the expression "poor CO2" does not automatically refer only to poor injection rate.


Hi ceg4048,
Is "poor CO2 implementation" a problem of distribution of the gas inside the tank ?


----------

