# Epsom Salt and kH relation



## Jaap (16 Mar 2015)

Hi,

will adding Epsom Salt increase my kH?

Thanks


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## Jose (16 Mar 2015)

Nope.

Epsom salt is MgSO4. Which in water dosociates into SO4 -- and Mg++, so this is what youll be adding.
KH is generated by CO3-- and/or HCO3-. This two come from things like Sodium bicarbonate (Na2CO3 I think), from the shells of molluscs, from limestone etc.


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## Jose (16 Mar 2015)

I forgot to say that Epsom salt will just change your GH, which is a measurement of the Magnessium and Calcium in your water.

So GH is Ca and Mg
Kh is Carbonates (CO3 and HCO3)


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## Christos Ioannou (16 Mar 2015)

Does it make sense to have the following scenario:

50% Water Change with tab water @ kH = 9

6 days after Water Change tank kH = 3
Thanks


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## Jose (16 Mar 2015)

Christos Ioannou said:


> Does it make sense to have the following scenario:
> 50% Water Change with tab water @ kH = 9
> 6 days after Water Change tank kH = 3
> Thanks



Are you using a soil like ada amazonia?
Have you added some kind of acid/ph buffer?
Do you do water changes frequently?

Basically KH is broken down by acids. This is one way to lower KH. So it depends if you added any source of acid.
CO2 does not change kh, only ph.


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## ian_m (16 Mar 2015)

You are probably being misled by test kits....They don't actually measure kH, but alkalinity. Alkalinity is also affected by things other than kH, ammonia, dead fish etc, so relying on test kit result is heading down the path to disaster.....


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## Christos Ioannou (16 Mar 2015)

ian_m said:


> You are probably being misled by test kits....They don't actually measure kH, but alkalinity. Alkalinity is also affected by things other than kH, ammonia, dead fish etc, so relying on test kit result is heading down the path to disaster.....


OK totally forgot about this thing with test kits & kH. Thank you


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## Jaap (18 Mar 2015)

How can I measure kH accurately to understand better whether the co2 pumped into my tank is mostly dissolved or mostly dissipated?


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## dw1305 (19 Mar 2015)

Hi all,





Jaap said:


> How can I measure kH accurately to understand better whether the co2 pumped into my tank is mostly dissolved or mostly dissipated?


 That is what the drop checker does. 

Because you know the "water" (really a dilute sol. of NaHCO3) in the checker is exactly 4dKH, changes in the colour of the narrow range pH indicator (bromothymol blue) indicate the CO2 level (based upon the experimentally defined equilibrium between CO2 (as H2CO3)) and bicarbonate (HCO3-). 

The air gap between the 4dKH solution and the tank water ensures that you are only measuring the H+ ion addition from CO2. 

Have a look at this thread for some more detail: <"pH drop & high alkalinity..">.

cheers Darrel


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## Jose (19 Mar 2015)

Actually you dont need to know the kh. The ph drop due to co2 is independent of the kh. This is why a 1 unit ph drop is recommended to get 30 ppm of co2 in the water. You are better buying a ph pen than anything else. Do a search on this topic specially at thebarrreport.com. If you aerate your tank through the nigh at the morning you measure ph. Then you have to lowe your ph to 1 unit less than that if you want 30 ppm of co2. You can push it further if you want with fish as indicators(dont recommend this myself).


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## Jose (19 Mar 2015)

The aeration at night has to be very good in order to gas ooff all the co2.


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## alto (19 Mar 2015)

Jose said:


> Actually you dont need to know the kh. *The ph drop due to co2 is independent of the kh.* This is why a 1 unit ph drop is recommended to get 30 ppm of co2 in the water. You are better buying a ph pen than anything else. Do a search on this topic specially at thebarrreport.com. If you aerate your tank through the nigh at the morning you measure ph. Then you have to lowe your ph to 1 unit less than that if you want 30 ppm of co2. You can push it further if you want with fish as indicators(dont recommend this myself).



It's likely The Krib is before your time but *the chemistry* still holds ...  KH, CO2 & pH are linked UNLESS you have some other dominant buffer in your system (occasionally observed/measured in hard water). 

Decent test kits (assuming a reasonable level of quality in water parameters) can be as good as the cheap membranes on those pH pens ... also changes in the reference solution as there is no sealed internal reference chamber in a cheap pH pen, & seldom any way to replace/maintain the internal reference solution, also very few people actually calibrate, clean or check the performance of their pH pens ... accuracy & precision is not what these quick, cheap pH monitors were designed for. 

I've run standard curves (using laboratory equipment)  & samples with Salifert & Seachem test kits & they perform quite well using local tap water, aquarium water from various tanks, RO/DI water as solvents.
Accuracy/precision certainly fell within reasonable limits for fishkeeping - as can most pH pens.
Of course there is always the disclaimer that perhaps I bought the only decent test kits in the lot & that present economy has led to lack of QC & performance in test kits aimed at the fishkeeping market, but one can still purchase those directed at the laboratory market ... some research into the reagent/reaction chemistry (including interfering compounds/factors) allows "test kits" to be used with reasonable expectations of data.


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## Jose (19 Mar 2015)

Kh affects the equilibrium ph but not the ph jump. This is fact. 

Ive gone through this fact a couple of times in this forum but 99% of people just dont get it.

http://www.ukaps.org/forum/threads/question-for-ceg4048.36402/page-4#post-392495

there are Tom Barrs links in the trhead I linked.


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## alto (19 Mar 2015)

Jose said:


> Ive gone through this fact a couple of times in this forum but 99% of people just dont get it


Yes I know this & agree that it's not as simple as it sounds ... but what is also true is that the amount of CO2 needed in soft acidic water to drop the pH by "1 pH unit" is reflected in that linked table (at the Krib)


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## Jose (19 Mar 2015)

Can you elaborate a bit Alto? Sorry i dont follow you. I suppose you mean the ph,KH table. The table linked shows the co2 concentration in the water.


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## alto (19 Mar 2015)

Yes if you take the time to really understand the chemistry (there are other discussions on this in various threads on the Krib - often Eric has them all linked in an archived discussion), you'll see why the table makes "sense" ... the main qualifier though is that while the carbonates are the dominant buffer in many water systems, there are also many instances in which other buffering compounds contribute.
So the various table are great as guides but not meant as "recipes".


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## Jose (19 Mar 2015)

Yes I agree with you. This is why measuring kh is such a bad idea with hobby grade test kits. If you know that you can measure co2 just by measuring ph then you have less error in your measurment.

So you could forget about kh, as long as its constant in your tank. This is mentioned in the krib and its the main source of error when  using the ph kh table for measuring co2. But you can rule this out.

So for whichever tank youll need a ph drop of around 1.1 to 1.2 units to get 30 kppms of co2 in the water. Why bother measuring kh if its another source of error?

There is a drawback with this method though. Its the equilibrium co2 concentration. We can only estimate it.


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## dw1305 (20 Mar 2015)

Hi all, 





alto said:


> It's likely The Krib is before your time but the chemistry still holds .


 I still like the Larry Frank article on the Krib as well, I've not seen a better explanation.

There is an Australian _Apistogramma_ keeper and chemist "Regani" who posts on <"Apistogramma forum"> (the Kribs successor) who understands pH, and when I have a chemistry question that I don't understand I usually ask him to explain it to me.

cheers Darrel


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## alto (20 Mar 2015)

Jose said:


> So for whichever tank youll need a ph drop of around 1.1 to 1.2 units to get 30 kppms of co2 in the water. Why bother measuring kh if its another source of error?


 Why do you think that the pH measure is so less prone to error than KH?


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## ian_m (20 Mar 2015)

Because kH is an indirect measurement. The test kits actually measure alkalinity and if using distilled water kH is related to pH. However you are using tank water and many other things present in the water will affect the test kit alkalinity reading thus giving a meaningless result.


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## Jaap (21 Mar 2015)

So basically a dropchecker with 4dkH water with bromeline blue if its yellow it means that I have adequate co2?


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## Jose (21 Mar 2015)

In that area yes. But it doesnt tell if your co2 keeps climbing during the day for example. This causes algae. A ph pen can tell you this and more accurately. Mainly a ph pen can tell you when co2 is stable and dropchecker cant.


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## Jaap (21 Mar 2015)

Ok....I think I get what you are saying but even if I have a climbing co2....thus throughout the add the co2 in my tank is increased....then why would that be a problem if I am over the threshold when lights are on?


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## Jose (21 Mar 2015)

Ive seen algae appear if co2 is not stable even if its at or over 30 ppm. When i keep co2 perfectly stable then algae does not grow.
Also its a lot more dangerous for your critters.


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