# Salinity and Water Hardness



## dwalstad (Apr 14, 2006)

The main question I'll start with here is that we want to increase water hardness so that plants get macronutrients Ca, Mg, K without adding a lot of NaCl. Also, I have advised people to use CaCl2 to harden water, not CaSO4 or commercial products that are loaded with sulfates.

To harden up softwater, I would not add Instant Ocean or marine salts. My mistake. Please read my book for how to increase hardness (p. 87), not my earlier APC post suggesting Instant Ocean. Yes, Instant Ocean provides Ca (370 ppm), Mg (1,200 ppm), and K (370 ppm), but it comes with way too much Na (over 10,200 ppm) and Cl (18,400 ppm). (Thank you Mysiak for getting me to rethink this.)

How much Ca do plants need? One expert aquatic botanist (Dave Huebert) wrote that the hardwater plant _Potamogeton pectinatus_ does fine in 2-40 ppm Ca. Let's shoot then for 10 ppm Ca for our plants with a big range either way.

Many aquatic plants are inhibited by 1,000 ppm NaCl (1 ppt).

As to problems from chloride (Cl), I don't see it at the levels required to increase water hardness. Since NaCl is 60% Cl, 1,000 ppm NaCl contains 600 ppm Cl. The federal government (USA) classifies chloride at 250 ppm as a secondary contaminant that may cause cosmetic or aesthetic effects in drinking water. EPA does not require enforcement of the standard; it's a guideline.

CaCl2 is 36% Ca and 64% Cl. If one adds CaCl2 to provide plants with 10 ppm Ca that adds only 28 ppm of Cl, which is much less than the 250 or 600 ppm we might think of as a possible threshold.

Most commercial products designed to increase water hardness contain only sulfates and no chlorides. When I asked one manufacturer, why they didn't use CaCl2 instead of CaSO4, they said that chlorides were toxic. Well, most anything is "toxic" if you use too much of it. I don't consider chloride toxic.

The scuffle over Cl overshadows the real problem-- sulfates. Sulfates cause problems in tanks with an organic soil substrate (e.g. potting soil). Sulfate-reducing bacteria convert sulfates to H2S, which is toxic at <1 micromolar (0.034 ppm). Since one sulfate converts to one H2S under severely anaerobic conditions, you don't want to load up the water with a lot of sulfates.


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## mistergreen (Mar 3, 2007)

Plants need sulfate too?
H2S oxidizes easily back to Sulfate, SO4 in presence of O2.


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## mysiak (Jan 17, 2018)

Crossposting this information:

Based on this study - The Acute Toxicity of Some Common Salts of Sodium, Potassium and Calcium to the Common Bluegill (Lepomis macrochirus Rafinesque) (https://sci-hub.tw/https://www.jstor.org/stable/4064450) it seems that using CaCl is really safer for fish. It doesn't evaluate long term exposure or impact on plants/substrate etc. at low concentrations though, so take it with a grain of salt. 

What I found interesting is that Sodium is actually less toxic than Potassium, always thought that it's the other way around.

"_The relative toxicity of the various salts was: NaCl<NaNO3<CaCl2<Na2SO4<Ca(NO3)2<KN03<KCl<K2S04. The relative toxicity of the cations was Na<Ca<K. The relative toxicity of the anions, based on the experiments with the sodium salts, was Cl<NO3<S04."_ (page 189 - summary).


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## dwalstad (Apr 14, 2006)

mistergreen said:


> Plants need sulfate too?


Yes indeedy. Plants need S, and in my opinion, it is a macronutrient. Table VII-2 (p. 105 in my book) shows the nutrient requirements of aquatic plants. Sulfur (S) is 800 ppm (mg/kg of dry plant tissue) and rivals that of Mg (1,000 ppm) and Ca (2,800 ppm).

To increase water hardness, I have always recommended making a MIX of both chloride and sulfate anions. That is the more natural condition.

H2S oxidizes easily back to Sulfate (SO4) in presence of O2.
Yes, but sulfates percolate into an organic substrate and get converted to H2S. Before it can diffuse into oxygenated water where it will be detoxified, this H2S inhibits and kills plant roots. I've heard enough anecdotal recountings of bottom-dwelling fish dying to say that H2S, which is highly toxic, doesn't get oxidized and neutralized as fast as one would hope.


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## dwalstad (Apr 14, 2006)

mysiak said:


> Based on this study - The Acute Toxicity of Some Common Salts of Sodium, Potassium and Calcium to the Common Bluegill


Mysiak and readers, please keep in mind that the toxicity of ammonia, nitrite, and H2S are all below 1 ppm. These are the real toxins. I would _never_ label Na, K, Ca, Cl, nitrates, and sulfates as "toxins." These are common salts, which of course, will cause problems at very, very high concentrations as shown in the table. [Or in the case of nitrates and sulfates, after bacteria--under anaerobic conditions-- convert them to the toxins nitrite and H2S.]


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## Doc7 (Feb 27, 2017)

Hello,

I see in the post you wrote to use p 87 and not the Instant Ocean recommendation for water hardness. At my case of 0 KH 0 GH shallow well water (which seems to be rainwater through sand with little minerals added) you had recommended increasing the overall ions. Am I misreading the post or is my case, which is not using I.O. "To raise hardness", also included in the recommendation to not use?

Here is the dosing I am adding, 11.5 g Instant Ocean in 40 G which is a bit less than half the 1 Tsp per 10 gallons I saw you write,










As seen here it adds about 0.8 GH at this rate:









And it seems the PPM even if it was 100% Sodium (which it's not as the Ca and Mg PPM in my above chart show, which agree with your data published elsewhere as well as the instant ocean website FAQ) , only brings overall to about 27 ppm Na which is within various drinking water guidelines I have found of 20-30 ppm.










I can re-run my spreadsheet and add a bit more CaCl2 and Epsom salt but would my water than lack the ions provided by the instant ocean, which I don't think are excessive (and anecdotally, I see plenty of posts on google search of people prophylactically adding some amount of salt to their planted tanks, not always with a reason provided. Not in the levels for brackish fish or illness treatment, and a lot more than what I am adding.)


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## mistergreen (Mar 3, 2007)

If you keep NaCl under 100ppm, you should be fine but make sure to do water changes and not just top offs. NaCl will build up over time as plants don't consume much of it.

The main ingredient in Instant Ocean I assume is NaCl, and smaller amounts in minerals. Ideally, you would want the other way around.


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## Michael (Jul 20, 2010)

One of the reasons NaCl is used in freshwater tanks is because it reduces the toxicity of ammonia. This is why all the tanks at Petsmartco have stickers saying, "We recommend Petsmartco Aquarium Salt". Personal opinion: this is cheating.


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## dwalstad (Apr 14, 2006)

Michael, NaCl is used to counteract nitrite toxicity, not ammonia toxicity (my book, p. 22). Cl- competes with NO2- for gill uptake and lessens nitrite toxicity. Chloride is very effective and explains why nitrite is not toxic in saltwater setups. (Folks, here's another reason to debunk this silly "chloride toxicity" business.)

DOC7, I'm getting lost in your reasoning and all the charts. If you added 11.5 g Instant Ocean to 40 gal (152 liters), that's 75 mg/ liter (11,500 mg divided by 152 liters = 75 mg/liter).

Even if *all* the Instant Ocean was NaCl, it would still put you below the plant inhibitory threshold of 100 mg/ liter NaCl. So It seems like what you have done is okay. My book advice is fine, but adding a _little_ Instant Ocean is better than nothing.

NOW, I remember why I used the Instant Ocean. Guppies like a little NaCl in the water. That's why I used it, but I did spike my Instant Ocean stock solution with additional CaCl2 and KCl. The other day, I also added a little MgSO4 to my stock solution.

We can go around this forever. But the only relevant question that I'd like to hear from DOC7 is: Are you getting the plant growth results you wanted??


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## Michael (Jul 20, 2010)

Thanks for the correction!


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## Doc7 (Feb 27, 2017)

dwalstad said:


> Michael, NaCl is used to counteract nitrite toxicity, not ammonia toxicity (my book, p. 22). Cl- competes with NO2- for gill uptake and lessens nitrite toxicity. Chloride is very effective and explains why nitrite is not toxic in saltwater setups. (Folks, here's another reason to debunk this silly "chloride toxicity" business.)
> 
> DOC7, I'm getting lost in your reasoning and all the charts. If you added 11.5 g Instant Ocean to 40 gal (152 liters), that's 75 mg/ liter (11,500 mg divided by 152 liters = 75 mg/liter).
> 
> ...


I sure am!!


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## dwalstad (Apr 14, 2006)

It shouldn't be such a struggle to get the bottom line, but sometimes it is. 

You have made my day!


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