pH Meter and/or Drop Checker, pH Levels / Profile

Jason Blake

1 Sep 2014

I have been reading many threads concerning the measurement of CO2 concentration in a tank. Unfortunately I am still a little confused about the matter.

On one hand I get the impression that all one needs is a drop checker and as long as it turns Limeade green, you have enough CO2 and of course an ability to read what the plants are telling through visual appearance. Nice and simple!

However I have been reading that it is important to ensure that the CO2 is at its maximum but stable levels either just before or as the lights come on for the day. This would appear to be a fundamental problem for Drop Checkers as they can only tell you what the CO2 level was an hour or two ago.

From my understanding people are using pH meters to record a pH profile. When the pH is at its lowest but stable level you have your CO2 at its highest stable level and therefore we are trying to get that drop in pH to occur at just before or at lights on, by adjusting when the CO2 injection begin before lights on, yeah?

I believe I should be aiming for a 1 point drop in pH if I was to go down this route. But I am confused as I am aware that depending on you KH (may have been GH I am sure I will be put right) you may not be able to drop the pH but a whole point due to the buffering induced by the KH. However if you take two water types at 2 different KH levels and inject the exact same amount of CO2 you will end up with the exact same amount of CO2 in the water but different levels of pH. So should I also be thinking about KH and/or GH test kits (I can't help but feel I am moving away from the zero test kit ethos and I can feel the wrath of god coming down on my head!) in order to ensure that I am not expecting the wrong amount of pH drop? Or is there where Drop Checker and pH meter can work in symbiosis? I.e. as long as I have a pH drop that is level and stable at lights on and a limeade green drop checker, is that the CO2 Sweet spot? I hope I am making sense?

Am I taking this too far? Should I just simply stick with making sure the drop checker turns limeade green during the photoperiod and leave it at that? Or is there any credence to investing in a quality pH pen and completing a profile to ensure the photoperiod and CO2 injection synchronisation is spot on?

Last question is about TDS. A lot of the threads/posts that mention pH meters also mention TDS. I am unfortunately completely lost with this. I think the jist is that TDS can affect the accuracy of a pH meter. I would really appreciate someone enlightening me about the TDS and if a meter that can read both TDS and pH would be better than just a pH meter on its own?

I understand that TDS is also an important measurement concerning fish breeding, however at this point I am not focused on breeding of any kind. This tank I am setting up is pretty much a warm up and a learning exercise for a planned much larger aquarium in the future.



Global Moderator
Staff member
15 Aug 2013
Lelystad, Netherlands
From my understanding:
Dropchecker can work, but 1) best to use a 4 KH standardized checker fluid, so we know the colorchanges 2) indeed it's a slow proces so just a check after the facts, 3) if all is working good then you can use a DC to see if you are still the same as yesterday
pH profile: 1) used to check the amount of CO2 in the water more directly, but more in relation to the levels during the day. 2) the amount of drop is indeed dependent on KH, 3) the level of CO2/amount of drop needed is dictated by the level of light 4) hard to say the actual amount of CO2 (don't use those colorcharts, very inacurate)
TDS: 1)pH pens work on electrical charges due to ions passing through a glass wall, with very little ions in the water (low TDS) pens are slow and more prone to mistakes (however in a profile it's more about the drop then the actual value) 2) TDS has influences on breeding due to the effects on the membrane of eggs and there is an influence regarding some plants that need low TDS (can't comment on that actual mechanism)


Expert/Global Moderator
Staff member
11 Jul 2007
Chicago, USA
I agree with Edvert. I think it's better to just keep it simple in the beginning. just use the DC in accordance with the instructions in the Tutorial, aim for a lime green color by lights on, monitor the plants and see how it goes. The DC is less accurate than the pH profile method but it is also easier to deal with.

It's much better to worry about flow, distribution and CO2 dissolution because there are inherent flaws in these techniques that force us to have to search for a better way to interpret CO2 concentration levels in the first place. Normally, if one goes through the trouble of a pH profile check, and if the check shows that there is a fault, then the usual suspects are flow, distribution and CO2 dissolution. So it's better to study best practices of accomplishing these things first. If executed properly you will find that there won't be a need for the more complicated procedures.

TDS is an acronym for Total Dissolve Solids. It really is just the concentration of all solutes dissolved in the water. That includes liquids. Since water is a polar solvent (meaning that the molecule has both negative and positive charges at different locations on the molecule) things that dissolve in it are also polar and therefore are also typically ionic, meaning that they also will become charged particles, which we call ions. Charged particles tend to more easily conduct electricity, and so, TDS is a term often used interchangeably with the term "conductivity".

Check for a primer regarding charged particles (ions).

You may also be able to read your municipal water report which should tell you what your hardness and alkalinity are. If you buy a DC with separate 4dKH water and reagent then you can always use the reagent to measure pH as long as the alkalinity is not too low.


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