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pH drop meeting resistance...

Courtneybst

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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.
6098C1CB-FD3E-447D-A795-06B04411A6B6.png
 

X3NiTH

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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.

:)
 

Zeus.

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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
 

X3NiTH

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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.

:)
 

Courtneybst

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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?
 

Courtneybst

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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.
 

jaypeecee

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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
 

Djoko Sauza

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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.
 

X3NiTH

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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.

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.

:)
 

X3NiTH

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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.

:)
 

Courtneybst

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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).
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.
 

X3NiTH

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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.

:)
 

Courtneybst

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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.
 

jaypeecee

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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
 

Djoko Sauza

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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.
 

jaypeecee

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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! o_O 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
 

jaypeecee

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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
 

dw1305

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Hi all,
the API KH Test Kit measures alkalinity and not actual KH*
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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