2 Calibrated PH monitor with different tank mesure?

Icefire · 04/28/2015, 02:30 PM

So I just received a used RKL and installed a brand new american marine pinpoint ph probe. Calibrated with 7/10 solution, cleaning in RODI in between.

Tank read 7.8.

I calibrate an old american marine pinpoint ph Monitor with an old probe with the same solution (was showing 8.05-8.22 a week before).

Once calibrated: PH 7.5

What give?, same solution, both read 7.00 and 10.00 in the solution but once in the tank or in a glass of water, I get a 0.3-0.4 difference in between.

I drip kalk 20 times a day so my PH should be near 8.

Any clue? Faulty PH Solution? I have many packet of the same lot but the Blue on the 10.00 are not all the same tint.

kurt_n · 04/28/2015, 09:44 PM

How old is "old" when you say it's an old probe? And did you verify both probes read 7.0 and 10.0 in the solutions after you calibrated them?

ca1ore · 04/28/2015, 10:29 PM

Swap probes between controllers and see if the 'error' follows the probe.

Icefire · 04/29/2015, 05:24 AM

Both probe calibrate correctly and read the 7/10 correctly too

the old probe is funny, left 5 years dryed in a bucked of sand and still calibrate good and quickly.

I bought a new one to replace it but I don't understand the less than 7.8 ph while dripping kalk...

ca1ore · 04/29/2015, 07:00 AM

An old probe, particularly if dried out, is unlikely to read accurately, even if it calibrates.

disc1 · 04/29/2015, 07:39 AM

The difference in salt content between the calibration solution and the tank water can have a big effect on how the probe reads. The old probe likely has a bad junction due to drying out. In the calibration solution ionic strength is relatively low so it doesn't cause much issue. In the saltwater the ionic strength is very high and the issue with the bad junction suddenly rears its ugly head.

ca1ore · 04/29/2015, 08:55 AM

As to why the good probe reads 7.8 I cannot say. Typically low pH is a function of either low alkalinity or excess CO2.

04/28/2015, 02:30 PM	#1
Icefire Seasoned reefer Join Date: Jan 2007 Location: In Quebec, Canada Posts: 3,653	2 Calibrated PH monitor with different tank mesure? So I just received a used RKL and installed a brand new american marine pinpoint ph probe. Calibrated with 7/10 solution, cleaning in RODI in between. Tank read 7.8. I calibrate an old american marine pinpoint ph Monitor with an old probe with the same solution (was showing 8.05-8.22 a week before). Once calibrated: PH 7.5 What give?, same solution, both read 7.00 and 10.00 in the solution but once in the tank or in a glass of water, I get a 0.3-0.4 difference in between. I drip kalk 20 times a day so my PH should be near 8. Any clue? Faulty PH Solution? I have many packet of the same lot but the Blue on the 10.00 are not all the same tint. __________________ Temp 80F, PH 8.5-8.0, Alk 6.8-7.2, Ca 430, Mg 1700, NO3 0-0.25, PO4 0.04, 34.4 PPT Lights @ 100% all others, 35% White Current Tank Info: 60g Cube, 120lbs live rocks, Hydra52 2x120W, 2 MP40+ 1 MP10 @ 70%, Phosban 550 GFO+Carbon, 200W Heater, SWC Skimmer, Kalk ATO, 150 gpd RODI

04/28/2015, 10:29 PM	#3
ca1ore Grizzled & Cynical Join Date: Apr 2006 Location: Stamford, CT Posts: 17,319	Swap probes between controllers and see if the 'error' follows the probe. __________________ Simon Got back into the hobby ..... planned to keep it simple ..... yeah, right ..... clearly I need a new plan! Pet peeve: anemones host clowns; clowns do not host anemones! Current Tank Info: 450 Reef; 120 refugium; 60 Frag Tank, 30 Introduction tank; multiple QTs

04/29/2015, 05:24 AM	#4
Icefire Seasoned reefer Join Date: Jan 2007 Location: In Quebec, Canada Posts: 3,653	Both probe calibrate correctly and read the 7/10 correctly too the old probe is funny, left 5 years dryed in a bucked of sand and still calibrate good and quickly. I bought a new one to replace it but I don't understand the less than 7.8 ph while dripping kalk... __________________ Temp 80F, PH 8.5-8.0, Alk 6.8-7.2, Ca 430, Mg 1700, NO3 0-0.25, PO4 0.04, 34.4 PPT Lights @ 100% all others, 35% White Current Tank Info: 60g Cube, 120lbs live rocks, Hydra52 2x120W, 2 MP40+ 1 MP10 @ 70%, Phosban 550 GFO+Carbon, 200W Heater, SWC Skimmer, Kalk ATO, 150 gpd RODI

04/29/2015, 07:00 AM	#5
ca1ore Grizzled & Cynical Join Date: Apr 2006 Location: Stamford, CT Posts: 17,319	An old probe, particularly if dried out, is unlikely to read accurately, even if it calibrates. __________________ Simon Got back into the hobby ..... planned to keep it simple ..... yeah, right ..... clearly I need a new plan! Pet peeve: anemones host clowns; clowns do not host anemones! Current Tank Info: 450 Reef; 120 refugium; 60 Frag Tank, 30 Introduction tank; multiple QTs

04/29/2015, 07:39 AM	#6
disc1 -RT * ln(k) Join Date: Sep 2010 Location: Little Rock Posts: 9,705	The difference in salt content between the calibration solution and the tank water can have a big effect on how the probe reads. The old probe likely has a bad junction due to drying out. In the calibration solution ionic strength is relatively low so it doesn't cause much issue. In the saltwater the ionic strength is very high and the issue with the bad junction suddenly rears its ugly head. __________________ David Current Tank: Undergoing reconstruction...

04/28/2015, 09:44 PM	#2
kurt_n Registered Member Join Date: May 2006 Location: WA Posts: 2,592	How old is "old" when you say it's an old probe? And did you verify both probes read 7.0 and 10.0 in the solutions after you calibrated them?

04/29/2015, 08:55 AM	#7
ca1ore Grizzled & Cynical Join Date: Apr 2006 Location: Stamford, CT Posts: 17,319	As to why the good probe reads 7.8 I cannot say. Typically low pH is a function of either low alkalinity or excess CO2. __________________ Simon Got back into the hobby ..... planned to keep it simple ..... yeah, right ..... clearly I need a new plan! Pet peeve: anemones host clowns; clowns do not host anemones! Current Tank Info: 450 Reef; 120 refugium; 60 Frag Tank, 30 Introduction tank; multiple QTs