# pH drop meeting resistance...



## Courtneybst (28 Dec 2021)

Hey everyone,

So after installing an Intaqo controller on my tank, it's provided me with some interesting data that I would have been none the wiser to.

My CO2 comes on 3 hours before the lights to try and achieve a 1 pH drop (or as close to). However, I've noticed that as the days progress since the last water change, there seems to be more and more resistance against the pH drop and the pH is increasing daily. I'm aware that some rocks influence pH slightly (I have Frodo/Millennium stone in this scape) but I just thought it was interesting.

Any ideas on whether this will negatively impact CO2 delivery? It's my understanding that in a higher pH you might never achieve a 1 pH drop so what is the acceptable drop in a higher pH? Is the pH drop completely irrelevant in this instance?

I've attached a graph from the last few days so you can see what I mean.


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## X3NiTH (28 Dec 2021)

You could probably do twice daily testing of the KH at the top and bottom of your CO2 profile for a week to correlate with the data seen in the profile trace, it will give you an idea of the impact the rocks have in buffering the system due to the low pH by added CO2. The higher the KH (buffer potential) the more acid (Carbonic) is required to move the pH.


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## Zeus. (28 Dec 2021)

One of the things I have against pH controllers is that you are at the mercy of the pH probe which can drift and also can be effected by other electric circuits nearby 😬. Which is why I go off the DC colour change and only use the pH profile to check the drift in on photo period. As we are only interested in the relative change and not the actual pH. The pH drift is just a proxy to check for [CO2] stability from lights on till CO2 off. The pH profile is also different on WC day, due to the dissolved CO2 in tap water


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## X3NiTH (28 Dec 2021)

Karl I don’t think this device actually controls via pH I think it only operates a timer to open a solenoid and the pH probe is only for monitoring the profile, I may be wrong about this, if so it’s not an issue for this device, if it were controlling then it would be hitting the set point daily but the equilibrium pH would still climb due to the rising KH, major risk to fish if it were. The profile certainly looks like it’s not being controlled.


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## X3NiTH (28 Dec 2021)

You know I think aquatics manufacturers are missing a trick by not automating the glass drop checker by adapting it to include digital pH colorimetry for profiling the CO2 ppm count.


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## Courtneybst (28 Dec 2021)

X3NiTH said:


> Karl I don’t think this device actually controls via pH I think it only operates a timer to open a solenoid and the pH probe is only for monitoring the profile, I may be wrong about this, if so it’s not an issue for this device, if it were controlling then it would be hitting the set point daily but the equilibrium pH would still climb due to the rising KH, major risk to fish if it were. The profile certainly looks like it’s not being controlled.


Yes the Intaqo controller starts and stops the CO2 based on pH measurements. 

Is there a KH test you recommend?


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## Courtneybst (28 Dec 2021)

Zeus. said:


> One of the things I have against pH controllers is that you are at the mercy of the pH probe which can drift and also can be effected by other electric circuits nearby 😬. Which is why I go off the DC colour change and only use the pH profile to check the drift in on photo period. As we are only interested in the relative change and not the actual pH. The pH drift is just a proxy to check for [CO2] stability from lights on till CO2 off. The pH profile is also different on WC day, due to the dissolved CO2 in tap water


Do you think I should just keep pumping the CO2 throughout the light period? That's what's currently happening anyway since the pH target is never being met, and therefore the valve never closes.


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## jaypeecee (28 Dec 2021)

X3NiTH said:


> You could probably do twice daily testing of the KH...


Hi @X3NiTH 

This makes me wonder how accurately people measure KH. If, for example, aquarists use the API KH Test Kit, the best resolution that it can provide is 0.5dKH using a 10ml tank water sample. On the other hand, the Tropic Marin KH Pro kit enables 0.1dKH resolution. I use this Tropic Marin kit when making up the KH4 buffer solution for drop checkers.

JPC


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## Djoko Sauza (29 Dec 2021)

jaypeecee said:


> Hi @X3NiTH
> 
> This makes me wonder how accurately people measure KH. If, for example, aquarists use the API KH Test Kit, the best resolution that it can provide is 0.5dKH using a 10ml tank water sample. On the other hand, the Tropic Marin KH Pro kit enables 0.1dKH resolution. I use this Tropic Marin kit when making up the KH4 buffer solution for drop checkers.
> 
> JPC


I don't know if all tests do, but at least the API KH Test Kit measures alkalinity and not actual KH. Many of the ferts we use raise alkalinity in water and therefore influence the result of this test - to which degree I don't know for sure. But add some (non-carbonate) ferts to RO water and you'll get a higher than expected "KH" reading.


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## X3NiTH (29 Dec 2021)

Courtneybst said:


> Is there a KH test you recommend?



I have been using the Hannah KH Pocket Checker colorimeter quite successfully. It has decent accuracy at 0.1 dKH.

Just measured my Tap water with it and I get a reading of 0.6 dKH (TDS is 33ppm). Testing my Tank water and it reads 10.4 dKH (TDS 430ppm). It appears as accurate for Freshwater as it is for Seawater.



Courtneybst said:


> That's what's currently happening anyway since the pH target is never being met, and therefore the valve never closes.



Informed that it does control based on pH but in this instance because the current needle valve setting is balanced for a lower KH buffering environment and due to the rise in KH it’s not able to reach target (I have run a controller like this never reaching set target, effectively not being controlled just open solenoid). You should only see an issue if you readjust your needle valve to increase the amount of CO2 added to get to the same pH drop but because your equilibrium point is shifting upwards due to rising KH then too much CO2 will enter the tank and could cause hypercapnia problems. You can’t run a pH controller successfully in the way intended in a tank that has fluctuating KH as you’ve found but if you never reach your target set point then you can still benefit from the monitoring. Ultimately your needle valve setting is controlling the supply  because you probably carefully had it set before you added a controller, if you had the needle valve completely open and unrestricted flow then your CO2 content will be increasing every day over the week and you would be seeing symptoms of hypercapnia.


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## X3NiTH (29 Dec 2021)

Djoko Sauza said:


> I don't know if all tests do, but at least the API KH Test Kit measures alkalinity and not actual KH. Many of the ferts we use raise alkalinity in water and therefore influence the result of this test - to which degree I don't know for sure. But add some (non-carbonate) ferts to RO water and you'll get a higher than expected "KH" reading.



I’m fairly sure that the Hanna KH colorimeter is only measuring carbonate hardness and not total Alkalinity because the colouring reagent appears to be displaying the spectral responses for Bromothymol blue and from what I am aware is that the reagent used is a blend of Bromothymol Blue and 0.1mol/L of HCl (folks using colorimetry based KH testing bots wanted a cheaper alternative to buying branded and wanted a DIY solution). I am not sure of the ratio of Bromothymol to HCl is but that could be easily calibrated for.


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## Courtneybst (29 Dec 2021)

X3NiTH said:


> you can still benefit from the monitoring


Yeah it seems like in this scape it will be useful for monitoring the pH but not controlling the CO2 since the KH is fluctuating. I think this is due to the type of rocks I'm using that are influencing the water chemistry. Conversely, I have the same controller fitted to a 350L tank which only uses inert dragon stone and Manzanita wood and the pH is pretty much stable the entire week. 

However, this tank is almost 4 times the volume and so it takes a lot of CO2 to shift the pH, and even then it never drops below 6.7. Despite this, the drop checker is the ideal colour and plants are growing well (bar a couple in the back).


X3NiTH said:


> if you had the needle valve completely open and unrestricted flow then your CO2 content will be increasing every day over the week and you would be seeing symptoms of hypercapnia.


This bit I don't understand, why would the CO2 content be increasing every day? Although the pH target isn't being met, the same amount of CO2 is being dosed daily as dictated by the needle valve and time schedule.


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## X3NiTH (29 Dec 2021)

If the needle valve was fully open or open further then you could be meeting that set pH point daily but as the KH would still be rising at the same time and thus the degassed equilibrium pH will also be rising the controller will still only close the solenoid when it hits its set point.

Say you intend to only have a 1 point pH drop daily then over the course of the week as the controller reaches its set point and the KH is rising the next period it could be 1.1 drop the next 1.2 and so on.


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## Courtneybst (29 Dec 2021)

X3NiTH said:


> If the needle valve was fully open or open further then you could be meeting that set pH point daily but as the KH would still be rising at the same time and thus the degassed equilibrium pH will also be rising the controller will still only close the solenoid when it hits its set point.
> 
> Say you intend to only have a 1 point pH drop daily then over the course of the week as the controller reaches its set point and the KH is rising the next period it could be 1.1 drop the next 1.2 and so on.


Ok yeah I understand what you mean now. That would lead to excessive CO2 levels by the end of the week.

If it's never reaching the set point however, I imagine the CO2 levels would be roughly the same every day? Since the CO2 is just turning on at say 2pm and turning off at 9pm with no variation or adjustment to the needle valve.


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## jaypeecee (29 Dec 2021)

Djoko Sauza said:


> I don't know if all tests do, but at least the API KH Test Kit measures alkalinity and not actual KH. Many of the ferts we use raise alkalinity in water and therefore influence the result of this test - to which degree I don't know for sure. But add some (non-carbonate) ferts to RO water and you'll get a higher than expected "KH" reading.


Hi @Djoko Sauza 

Many thanks for your feedback. That's _really_ useful. Out of interest, how were you able to establish that "the API KH Test Kit measures alkalinity and not actual KH"? Are you a chemist by any chance?

JPC


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## Courtneybst (29 Dec 2021)

One thing I overlooked is that I also recently increased my surface agitation and didn't adjust the CO2 to account for this. 

I've increased the output slightly and of course, the pH is dropping to adequate levels. I'll keep monitoring it since I find CO2 balancing takes a while.


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## Djoko Sauza (29 Dec 2021)

jaypeecee said:


> Hi @Djoko Sauza
> 
> Many thanks for your feedback. That's _really_ useful. Out of interest, how were you able to establish that "the API KH Test Kit measures alkalinity and not actual KH"? Are you a chemist by any chance?
> 
> JPC


Definitely not a chemist, a few posts here on Ukaps mention, it such as this one.

I am running a tank on pure RO at the moment and I get a KH result of 1 from this test kit. On top of that I'm using ADA Amazonia and tannin leaching botanicals, both of which reduce KH.

So my assumption is that it is measuring the alkalinity provided by the ferts.


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## jaypeecee (29 Dec 2021)

X3NiTH said:


> I’m fairly sure that the Hanna KH colorimeter is only measuring carbonate hardness and not total Alkalinity because the colouring reagent appears to be displaying the spectral responses for Bromothymol blue and from what I am aware is that the reagent used is a blend of Bromothymol Blue and 0.1mol/L of HCl


Hi @X3NiTH 

The latter half of your sentence above almost certainly explains an observation that I have made on a couple of occasions. And that is - my JBL 'Permanent CO2' reagent is slightly acidic!  Please read on...

I had 60ml of KH4.1 KHCO3 solution into which I dipped a recently-calibrated pH electrode. The solution measured 7.01/7.02. To this solution, I added 1 drop of JBL CO2 reagent. This lowered the pH to 6.88. A further drop of CO2 reagent took the pH down to 6.82.

JPC


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## jaypeecee (29 Dec 2021)

Djoko Sauza said:


> I am running a tank on pure RO at the moment and I get a KH result of 1 from this test kit. On top of that I'm using ADA Amazonia and tannin leaching botanicals, both of which reduce KH.
> 
> So my assumption is that it is measuring the alkalinity provided by the ferts.


Hi @Djoko Sauza 

Thanks for your reply.

I suspect that I need to pursue this with someone I know who is a Chemist by profession. That's if I can track him down.

JPC


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## dw1305 (29 Dec 2021)

Hi all,


jaypeecee said:


> the API KH Test Kit measures alkalinity and not actual KH*





X3NiTH said:


> I’m fairly sure that the Hanna KH colorimeter is only measuring carbonate hardness and not total Alkalinity because the colouring reagent appears to be displaying the spectral responses for Bromothymol blue and from what I am aware is that the reagent used is a blend of Bromothymol Blue and 0.1mol/L of HCl


I'd guess that it is still reading alkalinity.

<"Bromothymol Blue"> isn't specific to the carbonate  ~ CO2 ~ pH equilibrium, it is just a narrow range pH indicator. The reason that it <"measures" CO2">  in the drop checker is because of the air gap and "4dKH" solution, meaning that only a gas (CO2) can diffuse across the air gap and what the drop checker measures is the added H+ from the dissolution of the small percentage of CO2 that goes into solution as H2CO3 (H+ and HCO3-).

In the case of the Hanna colorimeter it is the known molarity and volume of hydrochloric acid (HCl) (the proton donor (H+)) which neutralises any alkalinity in the tank water, in a <"strong acid : weak base titration">.

It is the same principle that a drop checker uses, where the "4dKH" (sodium bicarbonate (NaHCO3) etc.) solution is the proton acceptor, and carbonic acid (H2CO3) is the acid added to the drop checker.

_* original quote by @Djoko Sauza _

cheers Darrel


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## jaypeecee (29 Dec 2021)

Hi @dw1305 

The first quotation above in Post #20 was not stated by me. I was quoting what @Djoko Sauza stated in Post #9. No big deal - just trying to avoid any confusion. Hopefully! 

JPC


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## H.Alves (30 Dec 2021)

I am also using the intaqo and what I did was to set the pH interval (in my case 6.2-6.3) and not kH, which I’m my case corresponds roughly to a pH drop of around 1. I can see that during the night, my tank does not fully degass since my degassed pH is around 7.2 or so and I am getting only around 6.9

I use a CO2 reactor and you need to open the valve more so you alway reach the target pH. I saw conflicting evidence whether it was better to have a continuous flow of CO2 (solenoid always on but low bps) vs bursts of CO2 (solenoid on with higher bps for small periods but several times a day).


As mentioned kH might as well change during the week with accumulation of fertilizers (depending of what you are dosing), leaching from rocks, etc.. so the values you reach each day might vary but probably will not have too much impact over a week time.

Also bare in mind that the kH/pH/ppm of CO2 charts are not very accurate since they do not account for all the other factors that do interfere with pH, like tannins, nitrates, etc… hence why people aim for 1-1.1 pH drop instead of following those charts.


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## jaypeecee (30 Dec 2021)

X3NiTH said:


> I have been using the Hannah KH Pocket Checker colorimeter quite successfully. It has decent accuracy at 0.1 dKH.
> 
> Just measured my Tap water with it and I get a reading of 0.6 dKH (TDS is 33ppm). Testing my Tank water and it reads 10.4 dKH (TDS 430ppm). It appears as accurate for Freshwater as it is for Seawater.


Hi @X3NiTH

Are you using the HI-772 colorimeter? If so, it is supposedly "Designed exclusively for saltwater aquariums, the HI-772 checker offers a quick, easy and highly accurate method of measuring alkalinity in degrees of calcium hardness, commonly abbreviated as dKH". And, something doesn't tally. Looking at the ratio of TDS to dKH for your tap water, it is 33:0.6 = 55. And, for your tank water, it is 430:10.4 = 41. Right now, I'm not sure what the explanation is for this. Rightly or wrongly, I was expecting the two ratios to tally. It must be something related to the composition of each water sample.

JPC


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## X3NiTH (31 Dec 2021)

Yes it’s the HI-772 for Aquariums and Marine Use and as you can see I’ve just used it successfully to test two vastly different freshwater parameters and gain an accurate result (in comparison to JBL Test strips ballpark values). Freshwater use titration tests for dKH on my tap give a reading between 1 and 2, this measurement is including the alkalinity effect of hydroxide moderation of the water to artificially increase the pH to Neutral for distribution network corrosion prevention, the use of the Hanna checker fluid being low molar HCl neutralises this component thus should only be measuring carbonate as a function of CaCO3. 

You have noticed that there isn’t a correlation between my tap values and the tank values and that would be because the tank is remineralised RO initially to a KH and GH of 8, TDS around 160ish at start and has been going a full year without water change while dosing EI, CO2 and overdosing Liquid Carbon (Microbe-Lift BioCO2), zero plant maintenance, all plant decay has remained in situ to become part of the total concentration of elements comprising the current water chemistry, hence increased GH, KH and TDS, I am not dosing calcium or magnesium, my Macro solution is undiluted BioCO2 dosed at 1ml/10L every other day fortified with added KNO3 and KH2PO4, all the chelates in use are biodegradable and non accumulative (DTPA, Gluconate, Humic Acid, Fulvic Acid and Citric Acid). No idea about the concentration of metal elements available but the snails seem not to mind it.


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## John q (31 Dec 2021)

Just a thought... cheapo tds meters and ph meters are fairly consistent at measuring changes, it's the consistency that counts, the actual reading is mmm, meaningless in a planted tank.  Again just a thought...


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## dw1305 (31 Dec 2021)

Hi all,


X3NiTH said:


> the use of the Hanna checker fluid being low molar HCl neutralises this component thus should only be measuring carbonate as a function of CaCO3.


New one for me, but it would make sense.


John q said:


> cheapo tds meters and ph meters are fairly consistent at measuring changes


Cheap conductivity (TDS) meters should be reasonably accurate (although ideally you would want a low range meter and automatic temperature compensation), but I wouldn't ever recommend a cheap pH meter.

cheers Darrel


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## John q (31 Dec 2021)

Fair enough darrel, I just worry that people new to this think they need to go out and buy the latest all singing, all dancing machines that will qive readings to the nearest 0.001.

If these high quality machines probes aren't stored or calibrated at each point of use(which they're often not) then the accuracy is lost, and they might as well buy a reasonably priced monitor and accept it will give satisfactory readings, albeit not 100% accurate.


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## Courtneybst (31 Dec 2021)

You can see what the graph looks like now that CO2 output has been increased. The 1.0 drop is being achieved, the drop checker is light green and the pH is stable from lights on 16:00-22:00.


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## X3NiTH (31 Dec 2021)

dw1305 said:


> New one for me, but it would make sense.



I’m being a bit naughty here because I’m making statements from assumptions based upon effect and trying to work backwards to find the cause. The device is designed to measure Alkalinity as a function of CaCO3 in seawater so that correct dosing of carbonates can be made to keep carbonate alkalinity stable in a reef system, as alkalinity has hydroxide as a component this would fudge the numbers and because the amount could be variable you would need to neutralise it to discover the alkalinity only as function of CaCO3 hence acidifying the sample with a consistent known total amount of acid (1ml reagent to 10ml sample), the resulting colour sample shifts from yellow to blue on the indicating spectrum depending on the hardness. I’m guessing at HCl being the acid in question only through comparison to what can be used if using a KH bot and we’re looking for a DIY route to inexpensive reagents, (for instance here on Reef2Reef).

Taking all this into consideration I’m making an assumption precisely because ‘it makes sense’. There will be a paper out there somewhere on this that would clear up any misconceptions but I haven’t found it yet or tried hard enough to look.


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## X3NiTH (31 Dec 2021)

Courtneybst said:


> You can see what the graph looks like now that CO2 output has been increased. The 1.0 drop is being achieved, the drop checker is light green and the pH is stable from lights on 16:00-22:00.



Be careful that if you’re KH is climbing during the week and you consistently hit the same pH by controller then by the end of the week the drop checker could be indicating yellow showing increased CO2 in the water.


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## Courtneybst (31 Dec 2021)

X3NiTH said:


> Be careful that if you’re KH is climbing during the week and you consistently hit the same pH by controller then by the end of the week the drop checker could be indicating yellow showing increased CO2 in the water.


Thanks, I'll keep an eye!


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## erwin123 (1 Jan 2022)

John q said:


> Just a thought... cheapo tds meters and ph meters are fairly consistent at measuring changes, it's the consistency that counts, the actual reading is mmm, meaningless in a planted tank.  Again just a thought...



I agree. For TDS, all I need to see is the trend up or down, though the movement does seem correspond to expected values.  When I measure TDS with my cheap meter before and after adding Epsom salts, for example, I find the TDS meter registering a fairly 'accurate' increase in ppm. Same when I add my all-in-one Fert.


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