# PH/KH/GH/Co2 problems



## dino21 (15 Jun 2021)

Hi,

Bit of a problem with our water and starting a new 60L  tank,    would appreciate some help  please.

Found that the tap water, which was always soft,  is PH 7.5 out of the tap,  but degassing down to PH 6.6 with a KH of barely 1dk   (just 1drop on Api test kit)  and  a GH of  barely 2.
This moring the tanks pH , with just the substate in, is down to 6.4 by midday and have just tried a new different brand KH test kit with the same results.

Our 3 year old tank with a standard aquarium gravel and sand  did hold the PH up to 7.6 before the daily Co2, with a KH of 3 and GH of 5 though that has dropped a bit as the tap water must have been getting softer over the months.

Know that the hardness need to be increased to keep the PH stable, but what is the best way to do that  ?  We will be using some well soaked wood  in this tank.

One other point we cannot quiet understand,  if the waters PH is naturally down at 6.4,  does that mean there is already 30ppm on C02 or Carbonic Acid  in the water, so we don't need to inject CO2  ?


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## dw1305 (15 Jun 2021)

Hi all, 


dino21 said:


> Know that the hardness need to be increased to keep the PH stable, but what is the best way to do that ? We will be using some well soaked wood in this tank.


Just forget about "pH stability", it is important for Marine Aquarists but <"soft fresh water"> never <"has a stable pH">, and it isn't a <"problem for most fish">.  

If you keep Lake Tanganyika cichlids, or <"hard water snails">, you need high carbonate hardness, and a stable pH (they go together).



dino21 said:


> One other point we cannot quiet understand, if the waters PH is naturally down at 6.4, does that mean there is already 30ppm on C02 or Carbonic Acid in the water, so we don't need to inject CO2 ?


You can only use the pH ~ CO2 equilibrium values with a solution of known dKH. You will have somewhere between 0.6 and <"3 ppm CO2"> unless <"you add CO2">. 

cheers Darrel


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## dino21 (15 Jun 2021)

dw1305 said:


> Hi all,
> 
> Just forget about "pH stability", it is important for Marine Aquarists but <"soft fresh water"> never <"has a stable pH">, and it isn't a <"problem for most fish">.
> 
> ...


Hi,

Thanks for those links to your previous posts, had not found them all before posting.
Not sure why our water has become so soft, know we live near the moorlands but would not have expected it to have changed so much over a year or so and do not believe we actually get it first hand?

Yes, we used to run a manine tank, hence getting hung up on hardness and ph, but todays few fish are just the usual communiuty fish.

There is one more twist to the problem and one I know from reading some of your other posts  you might again have some helpful comments, is that the new tank is being set up using Molar Clay and a silver sand topping as initially suggested by someone outside the forum.
They also suggested mixing in some pure moss peat with the clay, but with that and the possible tannins from the driftwood( though well soaked)  along with this now even softer water, do you think they could lower the PH too much ?
Might it be better to remove the peat before we start planting the tank  ? though believe the Molar Clay does not affect these parameters  ?


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## veerserif (15 Jun 2021)

Hello, fellow aquarist with very soft tap water! So long as my KH and GH is stable, I now completely ignore the pH reading since it'll naturally fluctuate as plants photosynthesize and use more or less dissolved CO2. For reference, my water out of the tap reads ~50μS, >3 dGH + >1dKH (it's been a while since I've tested), and pH 9.0 since the water plant treats it with lime. After 24h it settles at about pH 7. My tanks stay around pH 7.4.

I boost GH at water change with a commercial GH boost product, although I could mix my own with epsom salts and gypsum or calcium chloride. For KH, I keep a fistful of crushed coral in a mesh bag in my filter and also have some cuttlebone in the tank for my shrimp and snails to nibble. You could use crushed oyster shell, the kind sold as chicken feed, as a cheap alternative that will do the same thing. I don't actually have a target KH to hit, I just let it dissolve on its own and it will regulate itself in my experience.

Obviously if you are trying to keep extremely soft water ignore everything I just said!


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## plantnoobdude (15 Jun 2021)

LOW ph/kh is no problem, mine is well below 6 and 2.  i'd get the gh a bit higher in your tank, with a remineraliser, it could be plant uptake which is lowering your gh. I have a recent comment which explains how i make it if you want to know.

Anyone know where i can get TNC GH Boost?​


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## dino21 (16 Jun 2021)

Well now a little confused - as @dw1305  answer  and  his links  - did not seem concerned about those low values and neither do you two, @veerserif  and @plantnoobdude , yet you both up the GH and KH of your new water or via the filter. ?

So if a low ph is nothing to worry about,  in this context,  why should we be increasing the hardness, not sure what the purpose is  as from what DW says it does not affect the PH, if we understood correctly ?


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## dw1305 (16 Jun 2021)

Hi all,


dino21 said:


> yet you both up the GH and KH of your new water or via the filter. ?
> 
> So if a low ph is nothing to worry about, in this context, why should we be increasing the hardness, not sure what the purpose is as from what DW says it does not affect the PH, if we understood correctly ?


A lot of people run their tanks at very low carbonate hardness (dKH) values, have a look at @Roland 's <"Soft water tank">. There is also <"James' Planted Tank">.

In water low in solutes you can <"just ignore pH">, it isn't a very useful measurement as you get <"towards pure H2O">.

You need to add <"some dGH">, because both magnesium (Mg) and calcium (Ca) are <"essential nutrients for plant growth">.  My guess would be that, if you don't keep black-water fish, then having a nominal amount of dKH is beneficial.

If I was going to use water with no dKH I would definitely add <"some tannins to it">. 

cheers Darrel


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## plantnoobdude (16 Jun 2021)

@dino21
i keep kh low (0-2) , and gh around 10, exact number doesn't matter whether it be 20gh or 5gh if the Ca:Mg ratio is good.


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## veerserif (23 Jun 2021)

Yep, as the others have said, I add calcium and magnesium for my plants, as well as for my shrimp and snails. Adding KH (and therefore stabilizing pH) is more of a side effect of throwing in cuttlebone and crushed coral for the inverts.


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## ceg4048 (23 Jun 2021)

dino21 said:


> Know that the hardness need to be increased to keep the PH stable, but what is the best way to do that ? We will be using some well soaked wood in this tank.


Hello,
        The necessity of pH stability is another of those old wives tales. Neither plants nor fish care about pH stability and in CO2 injected tanks the pH varies wildly over the course of the day. As mentioned by other posters, the need to increase GH is driven only by the nutritional requirements of plants or possible inverts for magnesium and calcium, however, the required quantity of these is miniscule and one only needs to add enough to raise the GH by  1 or 2 points. The need to raise the KH is driven only by the need to be able to reliably measure the pH. pH probes and reagent kits need a carbonate hardness of about 3-4 to read properly.


dino21 said:


> One other point we cannot quiet understand, if the waters PH is naturally down at 6.4, does that mean there is already 30ppm on C02 or Carbonic Acid in the water, so we don't need to inject CO2 ?


This is the worst of all wives tales and hobbyists really suffer the consequences when they subscribe to this. The pH/KH/CO2 chart was never developed for aquariums and is more of a laboratory quick reference cheat sheet. The chart makes the following assumptions:
1. That the acid is the in the water is 100% carbonic acid due to a tiny portion of the gas reacting with the water.
2. That the carbonate hardness (KH) of the water is caused 100% by dissolved carbonate/bicarbonate.

These two conditions are easily met in a laboratory sample but are virtually NEVER met in real life for the following reasons:
1. Aquarium water and often, tap water always have some degree of dissolved organic and inorganic acid. We have no way of determining what percentage of the total amount of acid is carbonic acid, or how much of the pH is a result of the carbonic acid.
2. KH test kits CANNOT and DO NOT measure carbonate hardness. They are NOT carbonate hardness test kits, despite the fact they are labeled as such. They are ALKALINITY test kits. Alkalinity is defined as the ability of a water sample to resist change in pH. There are many water soluble substances, other than carbonate/bicarbonate which are capable of helping the water to resist a change in pH due to acid. Your "KH" test kit is incapable of distinguishing between carbonate/bicarbonate and these other substances, so it simply measures total alkalinity.

The implication, therefore, is that  both the pH value and the KH value that you use when reading the chart are completely corrupt and you will always read a higher CO2 content that is actually present if you use these measurements in the chart. Water that is sitting at equilibrium with atmosphere can only have, at most, approximately 8ppm of CO2. So you can see how far off you will be if you blindly use these two measurements in the chart.

Cheers,


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