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RODI, Equilibrium and Buffers

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  • RODI, Equilibrium and Buffers


    I have not been keeping an aquarium for long. I have a 40L desktop aquarium which is around 7 weeks old, planted (but not fully 'aquascaped'), I have cycled it using Seachem products and have been happy with the results on that front. I have quite hard tap water. Using the API drop tests for KH and GH, my tap water has 12 dKH and 18 dGH (12 and 18 drops). The PH of my tap water is around 7.3-7.4. My TDS meter reads the tap water as ~230ppm.

    It seems that most of the fish I keep and would like to keep in future prefer soft and slightly acidic water. I have also noticed several of the plants yellowing and stunted in growth which in my mind may well be down to PH and nutrient lockout etc. Based on this I decided to go down the RODI water route. Some people advise to mix with tap water until the desired GH is reached and then buffer products to get the specific KH/PH. To me it seemed that I may as well use a buffer product to set GH too which would avoid introducing nitrates and other pollutants from the tap water. I went ahead and purchased Equilibrium, Alkaline Buffer and Acid Buffer.

    Now it seems to be alluded to in other topics within this forum that the instructions and even calculator tools can be pretty hard to figure out. Why the calculator tools can't allow the user to work in either dKH/dGH or meq/L instead of making the user have to fiddle around doing the conversion with another tool is totally beyond me. Perhaps it just hasn't been considered yet? That would be an awesome addition to any app or website updates that roll out later :D

    Anyhow... I thought that I had the dosing process worked out, but I'm a little puzzled by my results so would like to check my working.

    I started with 15L of RODI water. TDS reading 0. PH unknown as my PH meter was jumping around all over the place. I presume this is due to lack of buffering and a drop test would be the correct thing to do. My target figures are 6 dKH, 6 dGH, PH 6.8. Using the DOSE app I worked out:

    Target = 2.15 meq/L (6dKH)
    Alkaline Buffer = 3g
    Acid Buffer = 1.82g (based on a linear scale between target PH 6.5 - 7)

    I first mixed the Alkaline buffer in a 1L jug until fully dissolved, then mixed it in with the rest of the 15L bucket. I repeated with the Acid buffer (took much more stirring to dissolve). I then turned over the 15L a few times with the jug in the bucket. After this I tested and got the following results:

    KH = 4dKH
    PH = 6.62

    Seems I missed the mark somehow. I used the DOSE app again, now using 1.43 meq/L as my starting number with 2.15 as my target. This time I decided to stick with PH 7 as a target to avoid adding any more uncertainty or cause for error. Based on this the app suggested I should add another 1g of Alkaline Buffer and 0.5g of Acid Buffer. Adding these to the bucket and mixing using the same process as before I got a KH reading of 6 which was the target but the PH was 6.7 not the target of 7. At this point I deiced to call it good as my scales are supposed to be accurate to 0.01g but who know how well calibrated they really are, therefore chasing a moving target and adding more and more product didn't seem like a good idea, I took a TDS reading which came out as 199ppm - this seemed higher than expected given my tap water comes out at 230 and is very hard.

    Next I added Equilibrium. Based on the usage instructions it seems the conversion between meq/L and dGH is different from that of dKH. The app called for 6.3g to be added to get to a target GH of 6dGH. I mixed this thoroughly for a good 5 minutes. Most of it was dissolved but there were still a dozen or so grains that would not. I got a result of 7dGH using my drop test. TDS at this point read 450ppm.

    This evening I came back and dipped the TDS and PH pens in to the bucket and got readings of TDS 550ppm and PH 6.68 so there has been some change in the water parameters. I didn't have the chance to take GH/KH tests but I presume from the change in TDS that the GH has probably risen.

    So my first question is what have I done wrong here that has meant I have missed my target - first for KH and then again for GH?

    Do I need to wait for a certain period after mixing everything before testing the water?

    Last of all, the 450-550ppm TDS reading of the water seems really high compared to figures I've seen discussed elsewhere which seem to be half of this or less, Keep in mind this water has not had any fertiliser or other treatments added. I was shocked to see the reading more that double my tap water TDS given that I'm trying to produce softer water. Perhaps this is normal and I've misunderstood something?

    Any help you can give me would be much appreciated. At this point mixing tap and RO water to produce softer water is starting to sound like a better idea!

  • #2
    Too much information? Sure would be great to get some guidance.


    • #3

      I have attached a dosing chart for you to reference using Alkaline and Acid Buffer! For a planted aquarium we recommend an alkalinity of about 1-2.5 meq/L (3-7 dKH). Your alkalinity is slightly higher than we would like for it to be. A KH that is too low will tends to be very unstable and very resistant to change. A KH that is too high tends to drag your pH upwards and hold it there. If your pH is too high, you will want to dilute the concentration of buffers (lower the alkalinity) in your aquarium. This can be done by doing small partial water changes with RODI water and/or doing water changes with an incoming water source that has the correct ratios of acid:alkaline buffer.

      We would not recommend mixing your tap water with RODI water because tap water typically contains phosphates that buffer your water to a certain pH. Acid Buffer and Alkaline Buffer are carbonate based buffers and do not work well with phosphate buffering ions to stabilize pH. Also, our dosing instructions are intended/the expected results with the use with RODI water so mixing the two will alter your results when dosing these products.

      I wouldn't be too concerned with TDS. Anything that you add to RO water will increase TDS. TDS is simply a measure of everything in the water that is not pure water. You could technically achieve a TDS with only Equilibrium, or only Buffering ions. The numerical value of TDS isn't as important as what is contributing to the total TDS in your water. A high TDS isn't bad if what is contributing to your high TDS is necessary for proper fish and plant health and growth.

      Hope this helps and let me know if you have any other questions!

      TechSupport SM


      • #4

        Thank you for the reply, I have only just seen it - not sure why I didn't receive a notification so I'll look in to that (perhaps in junk folder).

        I'm pretty torn between using only RODI water with buffers or mixing it with tap water to achieve the approximate desired GH/KH and then trying to use the buffers to tweak it. There is so much conflicting advice given on fish forums and in local shops etc.

        My local fish shop says they just use out local tap water (GH is high at 18 and KH at 12, PH is 7.5-8 - it also contains nitrates based on drop test, which is the reason I've started using RODI). They say it's not ideal for the fish but they can handle it ok; most of the tropical fish I want to keep are supposed to prefer softer more acidic water so KH/GH of 6-8 and PH between 6.5-7. Perhaps they don't really care because they'll just sell me more fish if they don't end up living very long.

        Another local fish shop which is part of a larger national chain say that they use a mixture of tap and RODI water to soften the local water to a more reasonable level.

        Then you have the fish forums. Many people on those advise to use a mixture of tap and RODI water - mainly based on the fact that they don't like spending money on buffers.

        One problem I have with using purely RODI water with buffers is the amount of water required for water changes every week. Initially I had read in several places that around ~20% water change every 1-2 weeks is required to keep nitrate levels down to those compatible with fish. I had even read that in well planted tanks where the plants are consuming nitrates it may be possible to do even less frequent changes. Then you have the advice I have been given in the tropical fish forums where several members insist that to have a healthy and well stocked aquarium I must change at least 50% water every week because the water in the aquarium contains lots of chemicals and compounds aside from the ammonia/nitrite/nitrates that we test for, plus bad bacteria etc.

        With my relatively small 125L and 40L aquariums that's still around 80L of RODI water that I need to produce and store each week, with another ~250L going to waste. In the summer months I can possibly collect the waste and use it in the garden which will offset the extra consumption a bit but in the cooler months it's just going down the drain.

        It's difficult to tell who is giving out good or bad advice - seems to be a steep learning curve for someone new to the hobby.

        With regards to dosing and the mobile app. Do you think it would be possible to have an option to use dGH/dKH instead of meq/L as I personally find this quite confusing to have to do the conversion every time I mix up a batch of water. I've made a mistake and wasted a batch of water because fo this at least once already.


        • #5
          Hello JBFUK,

          While there are many anecdotal reports on the internet by hobbyist who have successfully taken a specific approach to water preparation, there is not necessarily one right approach. For some hobbyist tap water might be the only option they have and make do with this, while others might invest in RODI units and strictly use RODI water. Whether you use only tap water, only RODI water, or half tap half RODI, there are ways to achieve ideal water parameters with your source water.

          - Only tap water: If you just use your tap water you may want to research fish that are better adapted to harder more alkaline water. It is true that some fish will "adapt" to the water you put them in but note that unideal water parameters can interfere with a fish's health, metabolic processes, nutrient transfer, etc.
          - Half tap half RODI: You could also use a mixture of your tap water and RODI water. Often times the best way to lower the GH and KH in your tap water is by diluting your tap water with RODI water to make it a little more manageable and easier to work with.
          - Only RODI: Using only RODI water will require buffers and remineralization, such as Acid Buffer and Alkaline Buffer for pH and KH, and Equilibrium for GH. But, once you obtain your target water parameters you will only have to dose these products once or twice a month, or during water changes. Note that all of our dosing instructions for our buffers and mineral supplements are intended for the use with RODI water. Those dosing instructions are the expected results when using them with RODI water. It is certainly possible to use things like Acid Buffer and Alkaline Buffer with tap water, however you will need to adjust your dosing amounts to account for any existing buffers and minerals already present in your tap water.

          So as you can see, there are certainly pros and cons to each approach and usually hobbyist will take the most economical approach when it comes to water preparation. The route you take will be tailored to what you can obtain/provide. Also, every system is different so the frequency at which you should perform a water change will also differ. An over stocked system will produce a lot more waste and require more frequent water changes than an aquarium with 1 fish in it. Additionally, an established tank with sufficient filtration should be fully capable of controlling ammonia, nitrite, and nitrate long term. So having plenty of bio-media, like Seachem Matrix, that supports the colonization and growth of aerobic and anaerobic bacteria and using chemical filtration medias like Purigen which controls ammonia, nitrite, and nitrate, should provide the filtration necessary to keep these compounds under control and reduce having to do emergency water changes to constantly lower nitrates.

          As a general rule when doing a maintenance water change we do NOT recommend doing more than a 30% water change. Large water changes have the ability to alter water parameters, alter macronutrient levels in planted tanks, stress tank inhabitants, and stress your beneficial bacteria colony.

          You can use the conversion 1 meq/L = 2.8 dGH/dKH when switching between the two, but I will certainly pass your suggestion along.

          Hope this helps and let me know if you have any other questions!

          TechSupport SM


          • #6
            Thanks, this is helpful. One thing that confused me about the meq/L / dH conversion is that the alkaline buffer instructions state that the conversion is 1meq/L:2.8dH but the Equilibrium instructions state that the conversion is 1meq/L:3dH. This led me to believe that the conversion is different for KH and GH. It seems this may just be an error on the Equilibrium packaging?

            I do have some other questions, mainly on how to use Matrix and Purigen in my filter (I have already purchased some but not sure on the best way to use with or instead of the media supplied with the filter). That's probably a topic for a different thread.


            • #7
              Hello JBFUK,

              What type of filter do you have? For optimal efficiency we recommend consulting your filters manual for the direction of flow of your water. After determining the direction, we would recommend the water flowing first through your mechanical, then through your chemical filtration, and lastly your biological filtration media.

              Mechanical: sponge, filter floss, etc
              Chemical: Purigen
              Biological: Matrix

              Purigen can be regenerated once it is exhausted. You can tell it is exhausted when you see a color change in the Purigen. It will go from its original color (blonde/off white) to a dark brown, almost black. To regenerate it please consult the Purigen regeneration steps:

              [Info: Purigen Regeneration Instructions](

              As for Matrix, when cared for properly Matrix will never expire or need to be replaced. We recommend to give Matrix a quick rinse in old tank water as a part of your usual filter maintenance. It is possible for Matrix to become impacted with detritus over time, reducing flow and capacity. In this case, it will require a thorough rinsing to restore it to full capacity.

              [FAQ: Where should Seachem filter medias go in my filter?](

              Hope this helps!

              TechSupport SM