# Soft or hard water ? What is better for plants ?



## kekon (Aug 1, 2005)

I know this topic was discussed by thousands of people many times but i'm somewhat confused.
I always used RO water reconstituted by different chemical compounds. There some recommendations concerning of how much calcium and magnesium should be in the water used for aquatic plants we grow in our tanks. For examaple, Seachem says that GH of 3..6 dGH is optimum. In literature i read that 6..10 dGH should be used. The "Fertilator" recommends 20..30 ppm of Ca. In turn, T.Amano keeps extremely soft water in his tanks (is it because some of ADA products PenacW or PenacC contains plenty of CaCO3 ?). In one of his interviews he said soft water is preferred by plants and they grow better when such conditions are met. Very soft water can lead to calcium deficiency very often but many people managed to grow great plants even in GH = 2..3. What do you think about it ?


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## OTPT (Sep 27, 2010)

> Advisable values are 3-4 KH and 6-8 GH


http://www.adaaust.com.au/support/support_maintainance.htm


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## kekon (Aug 1, 2005)

But they also wrote:



> For example, we advise using 50% tap water, with KH 8-10 and GH 15-20, with 50% osmosis water. *After about ten water changes, maintain a ratio of osmosis to tap water of 4 to 1*


If i get it correctly, if one mixes tap water of GH 15-20 with RO water in 4 to 1 ration then one obtains GH of 3..4. So it is unclear... 6..8 or 3..4 ?


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## Michael (Jul 20, 2010)

I don't think this question can be answered unless we know which species are being considered. Different species have different preferences.


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## Seattle_Aquarist (Mar 7, 2008)

Hi kekon,

When Tom Barr was in Seattle and did his presentation for GSAS I asked what hardness he recommended for growing most plants. He said he targeted a 5.0 dGH and didn't worry about his dKH.


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## OTPT (Sep 27, 2010)

kekon said:


> But they also wrote:
> 
> If i get it correctly, if one mixes tap water of GH 15-20 with RO water in 4 to 1 ration then one obtains GH of 3..4. So it is unclear... 6..8 or 3..4 ?


I expected you notice this. And I'm also a bit confused about it.

But why they advise starting with 6-8? Maybe they're afraid of too soft water also.

Either way, this surprises and also satisfies me in someway, I thought it was lower than this.
Now it's not incredibly low anymore.

BTW, I've just found the reliable source of info saying Brighty K is made from Potassium Carbonate.
May be they use that to counteract Aqua Soil.
http://www.adana.co.kr/product2.asp?seq=21 (please use Google translate)


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## kekon (Aug 1, 2005)

> I've just found the reliable source of info saying Brighty K is made from Potassium Carbonate.


Potassium Carbonate or Potassium Bicarbonate ? (K2CO3 or KHCO3 ?). The first one is extremely basic; i had problems with it. But KHCO3 worked well. K2CO3 caused stunting and precipitation of CaCO3 (water got cloudy in the tank)


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## OTPT (Sep 27, 2010)

탄산칼륨 = K2CO3
http://ko.wikipedia.org/wiki/탄산_칼륨

I thought about this too as I have read your thread about KHCO3. 
Don't have any comment though, I'm not Korean nor a chemist.


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## Diana K (Dec 20, 2007)

Most plants that we grow in our aquariums are quite adaptable to a wide range of GH, as long as it is not 0. They do need both Ca and Mg to survive. 

There are a few specialty plants that do not do well in water with too high mineral level. If you are growing any of these plants research and keep the parameters right where they need them. 

There are quite a few plants that can get the carbon they need from carbonates, if the CO2 is lacking. For these plants a KH over about 3 degrees is better. Usually, though, KH is used as a buffer when adding CO2, so the pH does not swing wildly high and low through the day.


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## kekon (Aug 1, 2005)

A few days ago a friend of mine forgot to add NaHCO3 when he reconstituted RO when doing water change. pH in his tank was decreased to 6.2. When that happened his plants started to grow better; Rotalla Walichii which was problematic plant now is growing quite well. Is it because of zero KH or low pH ? From what i know plants prefer slightly acidic water as micronutrients are better taken up by plants (especially iron and manganese) in lower pH.


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## AaronT (Apr 26, 2004)

I've always found softer water to be better. CO2 and other nutrients dissolve more readily and the plants just seem to thrive. At my old house the tap water was 1 kh and 10 GH. Now my tap water is 4-5 KH and 20 GH. I now mix 2:1 RO to tap water for water changes and do top offs with RO water. 

Also, in an acidic environment it's harder for ammonia to become a concern as it will be ammonium, which is safer for fauna and easily used by flora. This is why you get such a boost of growth when using a new Aquasoil setup. The ammonia is slowly released and the lowered pH lets the plants use it quickly.


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## AaronT (Apr 26, 2004)

kekon said:


> A few days ago a friend of mine forgot to add NaHCO3 when he reconstituted RO when doing water change. pH in his tank was decreased to 6.2. When that happened his plants started to grow better; Rotalla Walichii which was problematic plant now is growing quite well. Is it because of zero KH or low pH ? From what i know plants prefer slightly acidic water as micronutrients are better taken up by plants (especially iron and manganese) in lower pH.


Rotalas *love* soft water and low nutrient levels. They're one of the plants that always does really well when I neglect my tanks.


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## Bert H (Mar 2, 2004)

As one who has liquid rock (KH 9-10), I would say that softer water creates less problems. Hard water makes it harder to achieve optimum CO2 levels, and IMO, makes it harder, if not impossible, to run leaner tanks. It also seems that the few plants that need harder water, are not as popular as the ones who need the softer water. Ideally, I'd go for a KH of 3-4. GH, I don't worry about.


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## kekon (Aug 1, 2005)

I have two friends who both noticed that if they rise KH (so does pH) their plant look and grow better.
I wonder why it happens. From what i know Ca uptake decreases when pH drops, so maybe calcium is the case ? I'm really confused now...


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## Diana K (Dec 20, 2007)

We are back to....


It depends on the species of plant. 


While most average plants will grow in a wide range of conditions, there are some specialty plants that will only grow under a specific narrow range of parameters. If you are growing those plants at the edge of their tolerance, and something shifts your water more into the middle of their range then those plants are likely to grow better, faster, improved color... 


Another note: 
It is difficult for the home chemist (aquarium type) to make JUST one change to their tank. One thing that they know has been changed (oops, forgot to add this mineral or that...) can alter other things in ways you might not think about. Then the plants' response might be due to the first thing, that you know about, but that response might also be a results of any of the chain of reactions that happened because of that one thing. How can the home chemist (aquarium type) be sure of what is REALLY going on in the leaf that is suddenly pearling and turning show-quality red?


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## kekon (Aug 1, 2005)

> It is difficult for the home chemist (aquarium type) to make JUST one change to their tank. One thing that they know has been changed (oops, forgot to add this mineral or that...) can alter other things in ways you might not think about.


Yes, i'ts true.
It's almost impossible for example, to add only one chemical element to the tank. If we increase KH by use of NaHCO3 we also add sodium (in large amounts in many cases) which may have influence on potassium uptake. So we make two changes simultaneously: higher KH and more sodium.


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