Conversion factor for Hardness and Alkalinity (K)

[Jan Cavalieri]

Looking at our city's most recent water report they list the following:

Avg pH 9.4, Range 8.5-9.9
Avg Total Hardness (as CaCO3) 189, Range 110-282 ppm
Avg Total Alkalinity (as CaCO3) - 96, Range 47-138 ppm

The scale the website where I buy fish from lists the KH (which I believe is the total alkalinity?) in ranges of things like 3-12, or 2-6 etc. What is the conversion factor to convert ppm to whatever they are using - do I divide by 17 or something? When I do it looks like the buffering is pretty low. I found it interesting that they show hardness as CaCO3 and Alkalinity (which I understand to be KH) also as CaCO3.

If I look at other minerals that are adding hardness it's Chloride, Sodium and Sulfate - all of these minerals are from "leaching of natural deposits".

I haven't really paid attention when selecting fish as to the KH level tolerated by the fish (because the PH on the water report made sense while hardness did not) and I haven't lost a fish yet.

The numbers for one of my fish tanks is:

GH: 3 drops=50 ppm
KH 4 drops=50-100 ppm

So, If I understand this correctly - since I have low buffering power, the PH is going to be high and unstable? But if I do successfully reduce the PH and it is stable nearly every time I've done it (as I seem to have done) can I ignore the KH number since it only has meaning for a much higher PH (mine tap water measures off the API scale of 8.9)

Just trying to figure out what impact changing the PH has on that K value. Water is so damn soluable that it is difficult to understand how everything relates together.

 

[seangee]

There is a calculator on the site https://www.fishforums.net/aquarium-calculator.htm
pH does not actually matter to fish so there is absolutely no benefit in adjusting it. Hard water tends to be basic, soft water tends to be acidic which is why they have recommended ranges. But there are exceptions. What is quoted on sites like SF is usually the pH where the fish are naturally found. Fish are far more tolerant to long term pH changes than to hardness changes. The pH needs to be stable but (with very few exceptions) it doesn't matter what it is.

 

[Byron]

It may help to have some of the detail behind this. To first answer your question about conversion, the short way when it is converting degrees to ppm or the reverse is the number 17.9; if you multiply dGH or dKH by 17.9 you get the equivalent ppm. If you divide ppm by 17.9 you get the degrees. And just for reference, ppm is the same as mg/l which is common with water authorities at least in NA.

GH (general or total hardness) is primarily the dissolved calcium and magnesium. It is true that other minerals if present can increase the GH, but this is not likely ever going to be an issue as most of these have "safe" levels by law and you are not likely to see them this high in municipal water. The calcium and magnesium have no "safe" levels so they will be whatever the source water is. Water is a powerful solvent that easily and readily assimilates substances into which it comes into contact such as mineralized rock and organics. This is why freshwater, unlike the sea water in the oceans, can have very different GH, KH and pH depending where it occurs.

Of the three parameters GH, KH (Alkalinity) and pH, the GH is the most crucial for fish. Some fish cannot function normally without a minimum level of calcium and magnesium in the water, while other fish cannot function normally when these minerals are present in specific levels. Some fish species are somewhat more adaptable than others, and some have wider ranges than others. There are reasons for this that we need not get into here.

The KH has much less impact on fish, so much less that we can ignore that for our purposes here. The pH does impact fish to some degree, but generally only when it is either extreme or fluctuates. Generally a higher GH will also have a higher KH and pH, and the reverse.

You cannot successfully alter the pH without first dealing with the GH and KH. The KH serves to buffer the pH to prevent fluctuations, and this can be significant. But at the same time there is the natural biological process in any aquarium with fish where the buildup of organics causes natural chemistry changes. The breakdown of the organics by bacteria produces CO2, and this produces carbonic acid, so the pH tends to lower. However, this is governed to some extent by the GH and KH. So to answer your question about having a low buffering capacity and what this does to the pH...the p|H will tend to lower because there is nothing buffering it, once the buffering capacity of the GH and KH is exhausted. Regular substantial partial water changes help to stabilize this, another reason they are essential, and there is just no other way to deal with this natural chemistry/biology.

Chemicals that adjust pH may work immediately, but then the natural GH/KH buffering returns the pH to its previous level. This back and forth is severely stressful on fish and can kill them. This is why we say that a stable pH that is not too extreme in terms of being outside the species' preference is safer that one that is continually changing through our interference.

Generally speaking, if the GH is suited to the fish species, meaning it is reasonably close to what the individual species is biologically engineered to require to carry out its normal life functions, the pH will likely be fine. Changing the pH will not usually have any effect on the GH or KH, but understand this changing of the pH is only possible if the GH/KH are low enough to "allow" it.

Some water authorities in areas of soft water (which would normally have a low or acidic pH) do add substances to raise the pH. This is to prevent corrosion of the pipes and such. Depending what they add, it is often temporary, and has no effect on GH or KH.

 

[Jan Cavalieri]

Well they mention the source of all water contaminents - for example the source of copper is due to the erosion of old copper plumbing - but they don't do anything to remove it or adjust it.

So looking at our city's tap water our GH is approximately 11 with a range of 6.7 to 15.6 - while my fishtank is 2.8
The city's average PH is 9.4 and the PH of my tank (due to using PHdown) is 7.0. So PHdown did lower the General Hardness as well as lower the PH. It's interesting when you lower the PH in a tank (hopefully fishless) - I usually start with adding 2.5 mls of PHdown the first time (that's quite a bit) and it will bring the PH from my tap water level of 9 to about 8.5. If I add another 2.5 mls of PHdown the PH will go down from 8.5 to about 8. If I use a 3rd 2.5 mils of PH down it will suddenly lower the PH to 7.0 or even 6.8 so it's as if the buffering power ran out and dropped the PH level a huge amount. If you wait until the next day (which I always try to do) the PH may have rebounded some (which direction I never can predict) so it may go to 6.4 or jump to 7.5 where it will sit even through multiple water changes (perhaps due to the addition of Prime) so I quickly learned to take it really slow on that 3rd addition if I'm being very picky and want it to be close to exactly 7 (or 6.8 to 7.4 which are fine with me)

. The only time I've been drastically affected by water changes which (theoretically should bump me back up to 9.4) is when I cleaned out an ENTIRE tank including the substrate which I've done twice and it did bump the PH back up to 9 or higher again.

BUT a water change alone doesn't seem to bump the PH once. You would think, however, that an ordinary water change of say 50% would restore that buffering potential and it does, but it does it at the new PH that you set to (let's say somewhere around 7) rather than back up to the true water average of 9.4 so I rarely have it bumping the fish around.

I give up, I think I'll just start looking the their temperature requirement - then I KNOW none of my fish all require the same temperature - I have more problem with that than just about anything.

 

[Essjay]

GH measures only divalent metal ions so it doesn't include chloride, sodium or sulphate. It would include any copper 2+ ions, for example, but not copper 1+. TDS (total dissolved solids) includes everything, but GH doesn't.
When hardness is given as x ppm CaCO3, it doesn't mean that's the actual amount of calcium carbonate. It means "this is what all the divalent metal ions would be if they were all calcium carbonate". My younger son used to work for a water testing company and he explained what these tests actually mean.




My KH is 3. Many years ago I did have a pH crash but that was when I was very lazy about water changes. It was this that sent me in search of advice on forums - you can see I joined TFF in 2006 - and I discovered the crash was due to my infrequent, very small water changes. Since then I have done large weekly water changes and the pH has remained stable.