Does calibration fluid go bad? - The Planted Tank Forum
 
LinkBack Thread Tools Display Modes
post #1 of 10 (permalink) Old 03-14-2005, 04:26 AM Thread Starter
Planted Tank Obsessed
 
danmhippo's Avatar
 
PTrader: (0/0%)
Join Date: Feb 2005
Location: Taipei, Taiwan
Posts: 332
Does calibration fluid go bad?

After installing the pH controller, and calibrated with calibration fluid that comes with it. I found out my water's pH tested by the pH electrode is a notch lower than tetra's test kit and the Milwaukee hand held pH pen's reading. Where as the test kit shows 7.2 for the tap, the elctrode reads 6.8. The test kit showed my tank pH at 6.8, the electrode showed 6.5.

Could the pH calibration fluid go bad?

I calibrated my controller with pH 7 fluid, followed by pH 4 slope. The hand held pen showed the pH 7 calibration fluid as pH 7.2.

I am confused.

Now I don't know which one is correct. Is the tetra test kit wrong? Is the calibration fluid bad? Or if my hand held pH pen need calibration again? The pH pen has been in use for about 6 months without calibration.

Before I install the controller, I put my tank on the continuous CO2 injection. Now after installing the controller, with the same setting of bubble rate, I find 1/2 of the day without CO2 input because my pH electrode reads pH reached target level of 6.6.

I am puzzled if I should get a new electrode unit from pinpoint and their calibration fluid as well? I've heard good words about the accuracy of their electrode.

Also, Is the electrode responsible of reading the pH, or if the controller is responsible of interpreting the signal that sent back from the electrode and do the calculation at the controller? I am trying to isolate if it's a bad electrode, and if I should replace the electrode for a better brand.
danmhippo is offline  
Sponsored Links
Advertisement
 
post #2 of 10 (permalink) Old 03-14-2005, 06:25 AM
Wannabe Guru
 
shalu's Avatar
 
PTrader: (1/100%)
Join Date: Jan 2003
Location: San Jose, CA
Posts: 1,675
I think chances are the fluid is bad. I would get another bag of calibration fluid like PinPoints. There was another post not long ago about bad calibration fluid.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Flourite, wet/dry, AHSupply 302w PC, PinPoint controller

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
15w T6+15w T8

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
40w T6 ODNO4x, no CO2. Discus grow out.
10gallon Tonina tank, 2x15w T6 ODNO 4x
---------------------
I will do aquascapes after I collect all the plant species and grow them to perfection.
shalu is offline  
post #3 of 10 (permalink) Old 03-14-2005, 08:23 AM
 
PTrader: (0/0%)
Join Date: Feb 2005
Posts: 130
Oh dear, where to begin...

Instrument Accuracy
Instruments such as pH meters/controllers, test kits, thermometers and any other measuring instruments (even teaspoons and tablespoons), have a built-in error. The better the instrument, the more accurate, but there is ALWAYS an error. The Milwaukee SM122 controller has an error range, stated as an accuracy of +/- 0.2 pH units. The Pinpoint Controller, too, has an error range, though I can't find it on their website. A pH pen will most likely have an accuracy of +/- O.2 or greater. Needless to say, we can never measure pH EXACTLY with our measuring instruments, but we get close enough and close enough is good enough for our purposes.

Comparing Values
Knowing this, we can now see that comparing pH reading results, from different pH meters and test kits, and wondering which one is correct is useless and causes much needless consternation. If both meters have an accuracy of only +/- 0.2, then you could have two results that are as much as 0.4 pH units apart. This isnít wrong or bad, itís just the accuracy of our instruments and test kits.

Electrode maintenance
There are other variables that can ADD to the error already present in an instrument. One is the condition of the electrode. How old is it? When was the last time a calibration was checked and how fast did it get to pH 4 and 7? Is the electrode tip clean and free of algae or debris? Each of these variables can compound error upon error, so that accuracy is further diminished. Itís no wonder many plant aquarist, including Mr. Amano, donít use pH controllers at all, relying solely on a bubble rate and observation.

Accuracy vs. Consistency
Given all these variables that can affect pH readings, including the ďfreshnessĒ of calibration solutions (they expire), we can see that the CO2/KH/PH Chart becomes more of a guide and explains why some people, including myself, can maintain a ďtheoreticalĒ CO2 concentration of greater than 30 ppm with no apparent ill effects. Accuracy does not mean exactness, rather, itís a narrow range of error that comes with all measuring instruments and implements. So if your equipment is in good working condition and you are getting CONSISTENT readings from your pH controller, then I would trust the results, but only down to +/- 0.1 or +/- 0.2 pH units, For our purposes, consistency matters more than accuracy.

It appears that you are getting consistent results from your pH controller. The readings arenít fluctuating or drifting greatly and it sounds like you have no trouble in calibrating it. I would say your controller is functioning as it should given the accuracy of the instrument. Check your calibration solutions for an expiration date and get new ones if necessary. Used solutions should be dumped not saved as this can also compound more error into the accuracy of the controller.

I hopes this helps you and others in the same quandary. Just know that no two test results will be exactly the same, except perhaps by chance.
Gill Man is offline  
 
post #4 of 10 (permalink) Old 03-14-2005, 08:42 AM Thread Starter
Planted Tank Obsessed
 
danmhippo's Avatar
 
PTrader: (0/0%)
Join Date: Feb 2005
Location: Taipei, Taiwan
Posts: 332
Thanks folks, this inspired me that it is more important to observe livestock than relying on machines alone.

What worries me before, is that by deviating as little as 0.2 pH, the CO2 concentration could vary by large degree.

For example, My water's kH is 4 degrees,

KH 4, pH 6.8 = CO2 19ppm
KH 4, pH 6.6 = CO2 30ppm.

10 ppm difference of CO2 could very well being a bottleneck for plants' growth, and worse could lead to algae bloom. My problem now is if the controller/calibration fluid is off, then very possibly, my pH in the tank is only 6.8, which worries me if I am adding enough CO2 to the tank or not.

I am ordering a new batch of calibration fluid directly from American Marine Pinpoint, which with international mail should arrive in 2 weeks, just to confirm if the calibration fluid is indeed bad.
danmhippo is offline  
post #5 of 10 (permalink) Old 03-14-2005, 01:46 PM
Planted Tank Enthusiast
 
KevinC's Avatar
 
PTrader: (6/100%)
Join Date: May 2004
Location: Oshkosh, WI
Posts: 738
Quote:
Originally Posted by danmhippo
Thanks folks, this inspired me that it is more important to observe livestock than relying on machines alone.

What worries me before, is that by deviating as little as 0.2 pH, the CO2 concentration could vary by large degree.

For example, My water's kH is 4 degrees,

KH 4, pH 6.8 = CO2 19ppm
KH 4, pH 6.6 = CO2 30ppm.

10 ppm difference of CO2 could very well being a bottleneck for plants' growth, and worse could lead to algae bloom. My problem now is if the controller/calibration fluid is off, then very possibly, my pH in the tank is only 6.8, which worries me if I am adding enough CO2 to the tank or not.
But as Gill Man so eloquently stated above, your uncertainty in the pH measurement is 0.2 (and kH uncertainty is probably 0.5), so your kH could be as low as 3.5 or as high as 4.5 and your pH could be as low as 6.4 (when reading 6.6) or as high as 6.8 (when reading 6.6). So the only "safe" thing to say is that your CO2 is between about 17 and 42 ppm.

Personally, I'm a little surprised at the large range of error for the pH meters - that is as bad as a drop test kit! Is it really worth the extra money for the meter then?? In my labs we use scientific pH meters - accuracy is +/- 0.02 at the worst. However, we pay a lot more for both the meter and the probes. At home I use a drop test kit (personal hangup - I do enough chemistry at work, I don't want to do a ton of it at home) and I'm happy enough with the results. If in doubt, up the CO2 a little at a time and watch the fish for signs of unhappiness.

Kevin

Kevin

72g bowfront planted, CO2, 4x - T5HO, Eheim 2213 and 2217, 2 angels, pristella tetras, blue tetras, betta, albino bristlenose pleco, albino cories. Sword, vals, hygros, ludwigias, java moss and fern, anubias

2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.
KevinC is offline  
post #6 of 10 (permalink) Old 03-14-2005, 06:59 PM
 
PTrader: (0/0%)
Join Date: Jul 2004
Posts: 670
For months now I've been trying to figure out why my pH probe is off by between 0.2 and 0.25 pH every time I do the monthly calibration (using calibration points of 7 and 4).

The store even replaced the probe, thinking maybe I had a "bad" probe. They said that I shouldn't see such a difference: more like 0.05, or, with a new probe, almost no drift is normal...

So yesterday I calibrated again and the same result. I then used a liquid pH test on my tank water and got a pH equivalent to what the probe was saying before I calibrated.

Then, finally I had the brilliant idea to use the liquid pH test on the pH 7 calibration fluid. Guess what? it showed 6.8!

And I was wondering why I was starting to get BBA as I *thought* my CO2 was always at 30mg/l or above. But every month when I was calibrating the probe, I was actually lowering my CO2!

What I can't figure out is how over a month's time the probe moves back to correctly reading the pH?

By the way, the calibration fluid and the probe are both from Dennerle...
Laith is offline  
post #7 of 10 (permalink) Old 03-15-2005, 02:41 AM
Planted Tank Enthusiast
 
Whiskey's Avatar
 
PTrader: (1/100%)
Join Date: Feb 2005
Location: Vista, CA
Posts: 597
My PH meater, by Hanna instrumens (pen type model HI 98128) states that it is accurate on ph to 0.05 @ 65 DEG F. it also automaticaly compensates for temp and desplays the temp at an accuracy of 0.1 deg F.

Am I reading this wrong? or is this meater just better than most?

Thanks,
Whiskey

Current work in progress:

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Whiskey is offline  
post #8 of 10 (permalink) Old 03-15-2005, 04:21 AM
Planted Tank Guru
 
Betowess's Avatar
 
PTrader: (27/100%)
Join Date: Dec 2004
Location: Skagit County, Washington State
Posts: 3,199
For what its worth, with all the pearling which results from a high light, high CO2 tank... say 40 to 80ppm of CO2, I haven't seen any problems of too much CO2 for the fish, because there is so much O2 in the water column. So one can crank it up abit to control BBA - past the 30ppm threshold, with no ill effect, usually. I've read others who are more experienced than myself say this same thing and I have found it true myself. But I'm not using a controler and at night the calcium carbonate of oyster shells brings the pH back up abit, around .2 to.4 degrees over the course of the night. My only concern is this pH shift might be hard on the fish, but then it is over a 12 hour period of time. BTW, I really like my Hanna pHep 5 digital pH meter. I like it alot better than the Milwaukee,





Three Tanks...Eheim 2128 & XP3-90G, Eheim 2128-65G, Eheim 2232-25G.... Tek 4x54 watt T5-90G, Aqualight 96watt PC 65G low tech, 65 watt Aqualight-25G.... Hydors-90G & 65G ... Flourite in 90, 65, & 25 Gallons, .... Auto Water Change/Auto dosing on 90 & 65 gallon..... AGA member......
Betowess is offline  
post #9 of 10 (permalink) Old 03-15-2005, 04:27 AM Thread Starter
Planted Tank Obsessed
 
danmhippo's Avatar
 
PTrader: (0/0%)
Join Date: Feb 2005
Location: Taipei, Taiwan
Posts: 332
Quote:
Originally Posted by Betowess
with all the pearling which results from a high light, high CO2 tank... say 40 to 80ppm of CO2, I haven't seen any problems of too much CO2 for the fish, because there is so much O2 in the water column.
Level of O2 has nothing to do with CO2. And CO2 poisoning has nothing to do with how much O2 you have in your water.

It's either you are not adding too much CO2, or you have been really lucky so far, or you have faulty test kit that doesn't tell you what your actual pH and KH levels are.
danmhippo is offline  
post #10 of 10 (permalink) Old 03-15-2005, 10:07 PM
Wannabe Guru
 
shalu's Avatar
 
PTrader: (1/100%)
Join Date: Jan 2003
Location: San Jose, CA
Posts: 1,675
Quote:
Originally Posted by Laith
What I can't figure out is how over a month's time the probe moves back to correctly reading the pH?
Wow, you got a probe with self correcting feature What I am afraid now is if you get the good calibration fluid, you will start off right and off by 0.2 in a month(getting too much CO2). In that case, you are better off just to put the CO2 on a timer, not the controller


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Flourite, wet/dry, AHSupply 302w PC, PinPoint controller

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
15w T6+15w T8

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
40w T6 ODNO4x, no CO2. Discus grow out.
10gallon Tonina tank, 2x15w T6 ODNO 4x
---------------------
I will do aquascapes after I collect all the plant species and grow them to perfection.

Last edited by shalu; 03-16-2005 at 01:32 AM.
shalu is offline  
Reply

Tags
None

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the The Planted Tank Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome