Understand the main parameters of the aquarium water

Discus red spotted snakeskin

Discus Red Spotted snakeskin

As we have just seen in the first article, water is an important element to take into account for the maintenance of the discus.

The knowledge of needs This wonderful fish help I hope many people. This article discusses now a little more in detail the water parameters mentioned in the first pane (The water needs of the discus). The topic will be discussed more in depth ; with always designed to facilitate the understanding of terms sometimes …and

The subject enthusiasts find not here a "statement of chemistry" but an article which is accessible to most of us…

Because the understanding of the main parameters of water is essential to succeed with the discus.

When it comes to the water chemistry, many aquarists immediately evoke the pH. Gold to me, It seems more important to know first the «» hardness " (GH and KH) sound water.

First of all because the mineral salt water (hardnesses) plays a key role in the phenomenon’osmoregulation in fish; and then because the value KH This water will have a direct impact on the pH.

The latter will be explained in the article.

The hardness of the aquarium water, GH and KH

It comes from the mineral salt water, We talk here of the hardness KH and GH usually measured in Aquarium.

The KH or TAC of water…

It measures the amount of carbonates, bicarbonates and hydroxide of’water. Generally this «» hardness » is expressed in German degrees (KH). However in certain types of literature, You will find values in French degrees (TAC).

Keep in mind that 1 degree KH (German) = 1.78 French degree (TAC) and that 1 degree TAC = 0.56 degree KH.

Here I will speak in German degrees because the tests on the market use this unit. When we speak of KH, It also evokes the «» buffering capacity » water simply because the KH will have an influence on the pH. It is also for this reason that for lower the pH of the aquarium, should be initially measured sound KH.

More the KH is high and more sound buffering capacity is strong (Thus the pH will be high and stable)

Unlike, If the KH is low, the buffering capacity will be weak and the pH will be unstable (He can thus lower ; and that is what we are concerned to maintain the discus).

Of course, more the buffering capacity will be low (KH bottom) and most will need to monitor the pH… It may drop too low. (See the paragraph on the pH)

Role of the KH on the pH

The KH plays an important role on the pH

The GH or TH water…

She translated the amount in mineral salts from water.

Just like the KH, There is a German measure (the most used) but also French.

1 degree GH = 1.78 degree TH

1 degree TH = 0.56 degree GH

If the water in your aquarium has a GH of 7 degrees, sound TH is : 7 x 1.78 = 12.46 degrees of TH

We talk about water. hard "when the GH is high and "soft" water when it is low. As we saw in the first article (The water needs of the discus) the discus prefer water «» sweet " (At low levels in minerals)

Discus red spotted snakeskin albino

Recent varieties are more demanding, here a Red Spotted snakeskin albino

The pH of the water (Potential hydrogen)

It has a scale of 0 to 14 with 7 as a point of neutrality. Less than 7, the pH is said acid, greater than 7 It is said Basic.

This parameter is considered to tord (This commits only me) as 'the parameter the most important. Many aquarists are thus based on the pH to choose their fish or judging the State of health of their aquarium

The quality of a aquarium water is assessed by measurement of many parameters, pH is one of them and not only !

The pH a water In contrast to the «» hardness " (GH/KH) can vary very quickly ; in a few hours sometimes… As we have seen above, the KH here plays an important role. With a KH bottom (low buffering on the pH), It will take a small amount of’acid to lower the pH.

The first 'source d '.’acid "to take into account in a filtered closed circuit is the CO2. This gas produced by human beings living of l’aquarium (Bacteria filter, fishes, Plantes…) or added by man (diffusion of CO2) Once dissolved in water increases the acidification of the : pH decrease.

With this information, you will understand that the measure of pH is above your aquarium and not in your favorite pet store ; the water sample once shaken with the same amount of dissolved gas once to tucking

When one keeps loving species the waters low hardness (KH and GH low) like the discus ; a risk to consider is l’acidosis. The pH fall usually brutally and inconvenient them fishes or causes their death if nothing is done.

Rapid evolution of pH

The pH can change quickly

Nitrogenous substances, ammonia, nitrites, nitrates…

There are several types of nitrogenous substances which play an important role in l’biological equilibrium of the aquarium. Understanding of degradation of these processes is very important. It will allow you to not make mistakes that can be avoided easily.

In one aquarium, as in the nature, "nothing is lost.", does nothing, "everything changes".. I quote this sentence of Lavoisier because it perfectly illustrates the various transformations that take place through the filter of your aquarium.

But nitrogen contents are ?

These materials are present in the discus aquariums populated by beings living. They will find themselves in the fish excrement (partially digested proteins), in the urine (urea), in organizations dead (snails, fishes, nonfulfilment) uneaten food etc....

Thanks to the activity of bacterial colonies established mainly in the filter ; These pollutants will turn. One speaks then of the famous «» the nitrogen cycle ". This important data emphasizes the role of the filter in an aquarium. Because the masses of filtration (Bacterial media) contained in the filter will house many bacteria. Under their activity, ammonium will be oxidized nitrites then in nitrates.

Turn a little more in detail each of these data.

Ammonium / ammonia (NH4 / NH3)

As we can see in the the nitrogen cycle, the organic nitrogen turn as a first step in ammonium (NH4 ) / ammonia (NH3). This transformation takes place thanks to the activity of many bacteria. These chemical compounds are very toxic for our discus but they will not present in a balanced tank, equipped with a good system of filtration.

For imbalance, the presence’ammonia or (d)’ammonium varies in function of water pH. With a water to low pH, We will have the presence’ammonium (NH4 ) less toxic. With a pH up, will be l’ammonia (NH3) much more toxic. The discus will be less sensitive to the presence’ammonium If the pH is acid.

Aquarium with turbid water Dortmund 2012

Cloudy water can be a sign of presence of nitrogenous substances

Nitrite (NO2-)

Thanks to the work of bacteria, l’ammonium in turn will be transformed. The result will give the nitrites. This element is harmful for the discus to low levels. The presence of nitrites usually results in a respiratory distress in fish.

In one aquarium balanced, the content in nitrites is normally zero.

Nitrate (NO3-)

Here we come to the end of the nitrogen cycle. The organic nitrogen deteriorated in various elements. Here too is the "job" of many bacteria which will degrade the nitrites toxic in nitrates ; a far less dangerous element.

Indeed the discus tolerate (like others fishes) much better the presence of nitrates that l’ammonia or these nitrites. Despite all, the value of nitrates presented in a discus Aquarium should not exceed 25 mg/l. My observations allow me to affirm that the discus are able to temporarily move to much higher values ; but this makes our animals to stress, paving the way to possible onset of diseases and other disorders.

What you need to know, It is that the nitrates ; in an environment closed (as l’aquarium) accumulate over time. So, maintain a low content in nitrates are carried out through the attendance of the aquarist. Because he who, Thanks to the changes of water provided control value nitrate in the aquarium. L water’aquarium rich nitrates will be regularly removed to be replaced by water that is free. The regularity of these interventions will be the best guarantor of low in nitrates.

Attention however to the water used ! Some tap waters are rich in nitrates and please check the absence of this element before proposing it to your fishes. (If you use tap water for your discus Aquarium)

We just close the part dedicated to the nitrogenous organic matter and yet, it seems to me important to speak to a settings that all discussophile will meet one day at the heart of a reading or a discussion... the conductivity.

Discus blue diamond

Discus blue diamond

The conductivity of water,  un paramètre interréssant

As we have seen, There are several water parameters to measure when you wish to monitor the evolution of soundquarium in discus.

To avoid out of tolerance limits of the King of discus aquariums, This monitoring is essential. Measure all these parameters takes a little time ; and once installed routine, testing space, to forget, or do more…

In the parameters usually monitored, We have some that have an impact on the ability of water to conduct electricity.

Thus the values KH, GH or nitrates (among others) play a direct role in what is called the conductivity of water. The extent of the conductivity is carried out through a conductivity ; the result obtained by the equipment usually used in Aquarium is expressed as micro-siemens/cm2. This measure gives a quick indication of 'quality' of l’water.

This tool is very convenient to perform routine tasks ; as a measure of l’water dedicated to the partial renewal of the aquarium, the monitoring of the evolution of the tray (The conductivity evolving over time)

However, even if the extent of the conductivity of an aquarium proves to be very handy, the evolution of it is due to the variation of several parameters. Therefore to use the measurement of the conductivity to be responsive to an abnormal evolution. For the discus, the good development of the larvae is usually in the around of 100 micro-Siemens/cm2 (According to the species and varieties of discus) While the maintenance takes place between 200 and 800 micro-Siemens/cm2. However, these data cannot be critical at the foot of the letter because as explained a little high ; a set of parameters influence the conductivity and this should be taken into account !

Conductivity = KH / GH / nitrates / Phosphates….

Personally, I advise the use of the conductivity for the manufacture of water for the discus or the reproduction.

Test the aquarium water

The parameters that must be the subject of a follow-up are measured through several types "of tools.".

Among these, include them testing strips, the tests to drops or these electronic tests.

The testing strips have an asset in relation to the speed of measurement. It comes in the form of a stick with various small buffers. They will change color after a few seconds immersed in the aquarium water. The disadvantage of such a process remains its accuracy which is usually insufficient for the discus. Her Majesty is a demanding animal, It does not tolerate "the roughly"..

Test of water strips

Test bandelettes

The tests to drops are more accurate. The disadvantage of these tests will be linked to the measurement time. A nitrate test being for example "readable" after 15/20 min. (Time required reagents to give a result) However, I urge you to equip you such relatively reliable measurement tools. I would say even that is a minimum of equipment to have.

The electronic tests that exist under many brands will allow for example the pH measurement and the conductivity. Certainly more expensive to buy than a test drops, the electronic Tester many advantages. If the calibrations are fact, their accuracy is incomparable. Measurement is also interesting because it is enough of the plunge into the water and wait a few seconds to enjoy the result. Sooner or later, the informed discussophile team of this type of equipment.

Now, You can find on the market of electronic testsmore comprehensive as the one proposed by the brand Söll presented in the article " The new features in Interzzo 2012"

Test of water drops

Drops and electronic tests are recommended to monitor the quality of the water of the discus.

So, This article is going to end ; I hope it will help many of you to understand these some parameters of water. For those who wish to deepen their knowledge, I invite you to read the book of Renaud Lacroix " The water chemistry of the aquarium within the reach of all » to the editions Ulmer. You will find a large number of technical information on the theme with a very pedagogical approach. For my part, I give you venue for the third and final installment entitled "get from good water parameters for the. discus "

This article remains open to your questions and comments. I wish you pending, all the best with your discus !

About Author

Discus Breeder and Discus columnist, Yann Hoiret share on the website Fanatik-Discus his experience and passion for the King of aquariums. From 2014 He worked as a writer for the french magazine "AquaMag", the German magazines "Discus Live" and "Discus yearbook". He participated as an international judge in France Discus show 2014 and 2016 in Arvert, au Greek Discus Show 2014 in Athens, Discus Show in Paris Grigny 2015, 2017 and 2019, au FIDO concurso 2016, 2017 and 2018 Spain, au Nordic Discus Show 2018 Sweden, au France Discus Show 2018 Cognac, Discusvrienden the discus competition 2018, 2019, 2022 in the Netherlands.


  1. DEE ALAIN on


    I just found your site because I would like to throw myself into this passion and I wanted a tell you that your site is very interesting and super well done!!!

    Can you tell me or get bins of farms at the top and my first Discus (I of Namur in Belgium but I do not look at the km even if it is in France or in Germany.

    Regards ALAIN

  2. Yann Hoiret on

    Good evening,

    Thanks and glad you like browse Fanatik-discus !!! 😉

    Have you visited the site links page? The address of the Belgian forum "Waals discus" should help you to find contacts!

    Yann 🙂

  3. DEE ALAIN on

    Good evening,and Yann sell you the discus? Well to you ALAIN

  4. Yann Hoiret on

    Hello Alain,

    From time to time I reproduce some discus.

    You can see some in the "my discus".
    I perfected my strain in recent years already.

    Good read!


  5. Jean-Philippe on

    Hello to you. I commit myself to discus after years of break. I'm thrilled when I see the various strains and colors appeared in these 20 years. On the other hand, movers and being in a place (Haspengouw Belgium) where the GH tap is 39 degrees, I had to place a water softener. Therefore, I took a reverse osmosis unit and I remineralizes my water with salt Preis. I stand by my sub-adults with a conductivity 375. On the other hand, my KH is zero or almost. Apparently, Preis salt would be enough. I am amazed at the value of KH despite this salt. What do you think ?
    Thank you for your reply, and thank you for your great site. otherwise, congratulations on your superb specimens.
    Kind regards. Jean-Philippe

  6. Jean-Philippe on

    And thank you in advance for anything you do on your site.

  7. Yann Hoiret on

    Hello Jean-Philippe,

    Thank you for your comment and welcome to Fanatik-Discus!

    It always comes back to the discus… it is mythical!!! 🙂

    Actually your water quality is not really in line with the needs of the discus… You have opted for an interesting solution.

    Actually, the salts of the brand price goes back as the GH. It's normal.

    A good alternative for you would rather use the Dennerle brand (Remineral ) who was in the right proportions of KH and GH… My most interesting opinion.
    Having a low KH requires a very good follow-up of changes of water and pH… So few rights to the error.
    That is why only for maintenance, I prefer these mineral salts. When you have the chance to have a good quality tap water, There is not too many choices…
    If the tap water is 'just' very hard, a mix of osmotic water/tap water may be appropriate… Check, This is the case by case.


  8. Bastin Jean Pierre on

    Thank you for your efforts.
    Yes I would like to receive your information
    Beautiful day

  9. Yann Hoiret on

    good night and thank you! 🙂
    For this, I invite you to connect to Fanatik-discus site through a computer.
    When you visit the site, you on the right side of the screen; a tab "subscribe". (Tab does not appear on mobile browsing)
    You add your email address and especially, remember to validate your registration by following the instructions received.
    I'll see if I can do it for you.
    Keep me informed.

  10. Hi Yann,
    Great article and thanks for sharing.
    You mentioned that for the development of the larvae they need a water of around 100 micro siemens. Can you explain or confirm if we need to switch to a harder water and if yes,any explanation on this like the different stage of water. Thanks

  11. Yann Hoiret on

    Hi dwaine,
    Sorry for the delay…
    Yes of course, you can switch to harder water the young fry. In general, I do it between 7 to 15 days after free swimming stage.
    I switch around 250 micro siemens step by step.
    I always practice like this. But I never did real growth tests to mesure the difference between fry raised in low conductivity VS those breed In higher.
    Here I try to save as much RO water I can (Higher price water), and switching in this way give good results.
    I know several breeders arguing that a minimum amount of water minerals is necessary for the fry development. We should maybe call this « growing optimisation »…
    An other interesting field to explore… Looking in old books should be a good start.

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