Milwaukee pH Meter issues? Calibrating? - The Planted Tank Forum
 
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post #1 of 14 (permalink) Old 01-16-2005, 08:44 PM Thread Starter
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Milwaukee pH Meter issues? Calibrating?

Oye! Today's my first monthly maintenance, so pardon the few questions I've had to post today --

On my schedule of things to do, was to calibrate my Milwaukee ph meter, a recommeded procedure once a month.

When I got the Milwaukee meter last month, I calibrating it as instructed to 7.0 with the solution that came with the kit. I hooked it up to my CO2 tank, eased in to a steady 6.7-6.8 setpoint on the meter, and have been getting consistently steady 6.7-6.8 ph readings from my Aquarium Pharmaceuticals kit. Healthy fish, pearling plants.

Well, today I went to calibrate my ph probe with some Coralide pH 7.0 calibrating solution -- this is different than the original solution I used, which remember came with the Milwaukee kit. The Coralife is brand new, not yet opened, bought about 2 months ago -- no expiration date though. I removed the probe from the water, rinsed it in a solution of Coralife, and then took a measurement in a separate solution of Coralife. The pH meter jumped and stabilized to a whopping 7.6! Still, I took the little screwdriver that came with the Milwaukee and turned the calibration knob so that it read 7.0 while dunked in the solution. I rinsed off the probe with tap, placed it back in the tank, and the reading on the meter nose dived to 6.1 (remember, previous to this calibration it read 6.7-6.8 and my test kits confirmed this)

My Aquarium Pharmaceuticals kit is testing no where NEAR 6.1. I tried calibrating the probe again with another sample from a new bottle of Coralife solution. Same result. Call me crazy, but the tank water cannot be 6.1. With my KH of 4, that would be about 90ppm of CO2. Dead fishies.

SO what gives??

1) Bad calibrating solution? What brand do you folks use? Where do you order from? Got mine from Big Al's

2) Bad probe? (Seemed on target though when calibrated originally with calibrating solution that came with meter)

Are there any houshold products -- soda? -- that I could test the pH probe that have a known pH and wouldn't harm the probe.

For know, I'm going to set the meter back where it was. But I could use some answers to help ge tback on track.

thanks
steve
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post #2 of 14 (permalink) Old 01-16-2005, 08:51 PM
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I calibrate with the Milwaukee 7.01 solution. But when calibrating, I have noticed that I really need to wait 10-15 minutes in the calibration solution to make sure it's through moving. But the difference I see because of that is something like 0.1, not the 0.9 that you're dealing with!

Steve - 33g reef and a 180g planted in need of a re-scape.
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post #3 of 14 (permalink) Old 01-16-2005, 09:34 PM
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Ouch! The calibrating solution I'm using is something called "Pinpoint 7.000" and when I put the probe in it read --- 7.0. So I left everything alone. I've only "calibrated" once though, and the system has only been running about 6 weeks to two months.

Sláinte!
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post #4 of 14 (permalink) Old 01-16-2005, 10:10 PM
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You need to get some 4.01 calibration solution so that you can calibrate the slope. You need to do this, because as the probe ages its voltage signal deviates from its new condition. The only way to bring it back is to calibrate the low point. Also make sure that you're probe is clean. I usually remove it and clean the tip with a soft toothbrush under tap water. Here's a link to some real good info for your ph probe.

http://www.digital-analysis.com/pH_Probe_Service.htm

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post #5 of 14 (permalink) Old 01-17-2005, 01:37 AM Thread Starter
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Ouch is right! A couple things....

M. lemay,

Appreciate the advice. I've heard mixed opinions on this board having to calibrate the Milwaukee meter at both 7 and 4. Some say you only need to calibrate at 7 for aquarium use. In fact, even the instructions that came with the Milwaukee say don't bother calibrating with 4. I haven't heard anyone else using only 7 solution report this problem -- so it can't be merely because I didn't use the 4 solution. Or can it? Hmmmm.

This meter has only been in operation a month. Not sure how long it was sitting at the vendor, but it registered 7.0 with the Milwaukee solution that came with the kit -- and now, only a month later, it's registering 7.6 in Coralife solution. That's just too much.

Again, my water tests as 6.8 in my AP test kit. The calibrated probe is now saying my tank water is 6.1. Dead fish with CO2 if it was. It's not anywhere near 6.1

Maybe I need to call Milwaukee...
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post #6 of 14 (permalink) Old 01-17-2005, 03:13 AM
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Bad solution sounds more logical to me. You can try to use the test kit and measure the ph of the solution.

I have had my pinPoint controller for more than two years, never recalibrated, lazy me. But I am not concerned: one, the value of tap water is quite stable, two, my ph test kit agrees quite well.


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post #7 of 14 (permalink) Old 01-17-2005, 06:44 AM Thread Starter
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shalu,

yes, I was considering that -- trying to test the pH of the Coralife solution with my pH kit. Would I just fill my test tube vial with the solution and add the drops as usual? I'll post results.

I head ammonia has a pH of 10. I've heard some folks have dipped it in that to test accuracy, but that might be too strong on the probe.

In the end, I'll probably order another brand of calibrating solution.
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post #8 of 14 (permalink) Old 01-17-2005, 06:05 PM Thread Starter
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Spoke to technical support at Milwaukee, a very frank gentleman who said without reservation or hesitation the problem is the Coralife solution.

"We make instruments, they don't" meaning Coralife's solution is neither exact or up to par. Sounds like they had this problem before.

I'm going to purchase some Milwaukee pH solution since I had no problems with that the last time.

I post this for other's benefit.

Thanks
Steve
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post #9 of 14 (permalink) Old 01-17-2005, 06:26 PM
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I suspect it's your solution as well.

I've had no problems with Pinpoint's 7.000 pH solution.
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post #10 of 14 (permalink) Old 01-20-2005, 09:43 PM Thread Starter
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for those of you using the Pinpoint brand of calibration solution, are you using it with a Milwaukee pH meter, and, if so, without problems?

thanks
steve
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post #11 of 14 (permalink) Old 01-22-2005, 11:44 PM
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Sorry to hijack. But would using distilled water with a pH of 7 work, too?
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post #12 of 14 (permalink) Old 01-23-2005, 02:38 AM
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I'm using the pinpoint calibration solution on the Milwaukee pH controller only. Can't see why it would present problems with a pH monitor. The 0.000 resolution is a very fine degree.

Pure water is very unstable. Definately not something to calibrate with. Plus it won't have a pH of 7 since CO2 from the atmosphere lowers it - much more then in an aquariums since it lacks a buffer.
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post #13 of 14 (permalink) Old 02-07-2010, 06:07 AM
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in my experience it is VERY important to adjust the slope of a Milwaukee pH controller when calibrating. Also cleaning the probe as m.leamy said is VERY VERY important. My Milwaukee pH controller experienced a drastic reading change just from cleaning the probe. I also found the slope to be .4 off when using 4.0 solution. The cleaning and slope become more important if the probe is over 6 months old. My probe is nearing the end of its life according to this:

The question most asked about the Milwaukee SMS122 pH/co2 controller: What is the life expectancy of the "replaceable probe?"
Answer straight from the folks at the factory:
Ph probes are a consumable item just like a light bulb. Over a period of time the electrolyte solution becomes so low that a proper read can not be done. The average life is 18 to 24 months so, at this point I would guess that you probably have a dead probe.

You can check the strength of your probe by putting the probe in Windex with Ammonia and the display should go to 10.0 or higher. If your unit can not go to this point then you need to replace the probe and get new calibration solution.

You should calibrate your unit about every 2 to 4 weeks. Calibration solution is not expensive and it assures accuracy.

Best regards
Milwaukee Instruments Tech Department

http://www.aquariumplants.com/product_p/pr1315.htm

I think I'm going to go with a pinpoint probe this time due to the fact that i cant stand the yellow color of the Milwaukee probe. You seriously cant hide the thing lol.


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post #14 of 14 (permalink) Old 02-16-2010, 09:11 PM
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Quote:
Originally Posted by Raul-7 View Post
Sorry to hijack. But would using distilled water with a pH of 7 work, too?
You would think so but the lack of ions in distilled or RODI water makes the readings very unreliable.

I have the milwaulkee probe and I calibrate it with baking soda dissolved in a glass. Should be right on 8.2 which works well for testing reef tanks which are typically 8.2-8.5

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