Quote:
Originally Posted by hockeyfan
I measure with a milwaukee ph meter, half halve of a glass top on for a lid, and no Ca reactor
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To start with, you need to remove anything (the lids) that prevent good air circulation at the surface of the tank. You might consider putting a fan in a position where it can blow across either the surface of the tank or across the surface of the sump, and start aggresive skimming 24/7 to both increase air exchange and to improve the removal of organic substances that might otherwise increase the pCO2 of the water as they decompose in the water column. If at all possible, run a 1" air hose to the outside to pull in outdoor air to the skimmer's air inlet, in order to improve the removal of CO2 from the water column by dropping the % CO2 in the skimming air, and to provide a higher O2 content (although O2 content has little to do with the actuao pH of the tank, it will improve the total gas exchange in the system and help degass the CO2, which is mostly responsible for your dropping pH values). Do a search on a carbon canister for the air intake outdoors to prevent accidental intake of potential toxins by the skimmer, just as a precaution. Your issues with low pH are probably a combination of meter error as well as potential accumulation of CO2 gas in your tank, a common issue with tanks lacking a good source of gas exchange at the surface.
For the pH meter itself, you need to test its calibration using the 20 Mule Team Borax test to check your meter. All meters will drift from calibration, showing false values for the actual pH of the water column unless recalibrated and cleaned, and the Milwaukee meters are known to drift from calibration rather quickly (personally recommend the Pinpoints to prevent rapid drift from calibration). See
this link for the use of the borax test as well as some info on cleaning and calibrating meters that fail the borax test.
You use the 20 Mule Team Borax test because
even if you do a poor job of making this solution, it will almost always be at a pH of 9.18 + 0.02 using a meter in calibration and functioning properly, so it is a great test to test the functioinability of the meter as such. In this manner, you can test the ability of the meter to correctly read a known value of pH: if it is off by
+0.04 or more, then you know the meter is in need of recalibration, or the probe's fluids are off, the probe is damaged, or too old to correctly measure pH.
Use the Borax test to see if the meter will read the pH of a broad response sodium borate at the right pH level. This evaluates the ability of your probe to read pH correctly. If your probe cannot pass the probe test with
sodium metaborate (20 Mule Team Borax), then it is time to do the cleaning of the probe and attempt recalibration again, and if it still will not pass the borax test, it's time to replace the probe.
Calibration is good, but it is always a good idea to do a separate test with the borax to see if your meter is testing well during normal continuous usage. I read with interest Craig Bingman’s posts circa 1996 about a problem with (not named for this post) brand of Ph
calibration solution where the pH 10 standard was off by almost a full pH unit. Craig had purchased a few packets of this particular brand, used a lab bench electrode, calibrated with fresh research-quality pH standards and tested these calibration fluids. After much discussion, Craig proposed that folks use a freshly prepared buffering solution of sodium metaborate that will always come to the same value under home conditions to check the quality of their calibration work. This lead to the publishing of his article in Aquarium Frontiers on the use of 20 Mule-Team Borax to prepare a home standard solution. I would suggest that you use this procedure to make sure that your pH probe and meter are in actuality measuring what they are supposed to.
Essentially, this involves making a standard solution of borax in RO/DI water. This differs from NIST standard solutions in that NIST solution standards rely on using controlled measured amounts of an acid and its conjugate base. Usually you would need to mix precise quantities of two different solutions to make a pH standard solution in a precisely measured volume. These will have a set shelf life, and will deteriorate more rapidly if exposed to less than ideal conditions.
Rather than try and make these lab standards (you could, if you had the precision lab ware needed to measure end volume and the acid and conjugate base weights), we can use the properties of sodium metaborate in water to form these equimolar acid/conjugate bases for us (Boric acid and hydrated borate ions). This is one of the advantages of using borax as a testing standard.
Quote:
pH of Sodium Metaborate Standard Solution at Various Temperatures
(3.80 grams Na2BO7 10H2O/liter)
Degrees Celsius . . . Degrees Fahrenheit . . . . . . pH
0 . . . . . . . . . . . . . . 32.0 . . . . . . . . . . . . . 9.464
5 . . . . . . . . . . . . . . 41.0 . . . . . . . . . . . . . 9.395
10 . . . . . . . . . . . . . 50.0 . . . . . . . . . . . . . 9.332
15 . . . . . . . . . . . . . 59.0 . . . . . . . . . . . . . 9.276
16 . . . . . . . . . . . . . 60.8 . . . . . . . . . . . . . 9.266
17 . . . . . . . . . . . . . 62.6 . . . . . . . . . . . . . 9.256
18 . . . . . . . . . . . . . 64.4 . . . . . . . . . . . . . 9.245
19 . . . . . . . . . . . . . 66.2 . . . . . . . . . . . . . 9.235
20 . . . . . . . . . . . . . 68.0 . . . . . . . . . . . . . 9.225
21 . . . . . . . . . . . . . 69.8 . . . . . . . . . . . . . 9.216
22 . . . . . . . . . . . . . 71.6 . . . . . . . . . . . . . 9.207
23 . . . . . . . . . . . . . 73.4 . . . . . . . . . . . . . 9.198
24 . . . . . . . . . . . . . 75.2 . . . . . . . . . . . . . 9.192
25 . . . . . . . . . . . . . 77.0 . . . . . . . . . . . . . 9.180
26 . . . . . . . . . . . . . 78.8 . . . . . . . . . . . . . 9.172
27 . . . . . . . . . . . . . 80.6 . . . . . . . . . . . . . 9.167
28 . . . . . . . . . . . . . 82.4 . . . . . . . . . . . . . 9.155
29 . . . . . . . . . . . . . 84.2 . . . . . . . . . . . . . 9.147
30 . . . . . . . . . . . . . 86.0 . . . . . . . . . . . . . 9.139
35 . . . . . . . . . . . . . 95.0 . . . . . . . . . . . . . 9.081
40 . . . . . . . . . . . . . 104.0 . . . . . . . . . . . . 9.068
Characteristics of Sodium Metaborate pH Standard solution
Characteristic . . . . . . . . . . . . . . . . . . . . . . . . Value
Composition(gm Na2B4O7 10H2O/1000 ml) . . . . . . 3.80
molality (m) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.01
Molarity (M). . . . . . . . . . . . . . . . . . . . . . . . . . 0.009971
pH at 25 degrees Celsius . . . . . . . . . . . . . . . . . 9.180
change in pH after dilution
to half original concentrationin water .. . . . . . . . +0.01
Temperature coef.
dpH/dt,unit degrees Celsius-1 . . . . . . . . . . . . . -0.0082
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data taken from C.Bingman Aquarium Frontiers article
These tables give the properties of differing temperatures on the pH of borax (sodium metaborate) in purified water and the resulting pH, as well as the characteristics that allow us to demonstrate the relatively small change that varying the concentration of the solution has on pH when compared to the standard solution. To make the textbook standard, you dissolve 3.8 grams of borax per liter water using a lab balance and a volumetric flask. Fortunately 1/2 level teaspoon of solid borax weighs just about two grams, AND the pH of borax solutions is only weakly dependent on the concentration of borax in the solution (SEE CHART), SOOOOOooooo, we don’t need to be tremendously precise in our measurement of the borax to still produce a relatively accurate pH standard. We can make a useful product here without the use of a lab balance nor a volumetric flask.
Use a pint of water (473ml) and add a half teaspoon (1/2 level tsp.) of borax to make a resultant pH standard solution with about 2 gm of sodium metaborate per 473 ml or 4.3 grams of sodium metborate/litre. Although using this method to make the standard will only result in an accuracy of about plus or minus 10% of the lab standard sodium metaborate pH calibration solution, there is such a weak dependence of pH on concentration of the solute buffer here that it is close enough for our purposes. To use this solution, calibrate your system with your bought standards, allowing 10 minutes for equilibration at both set-points, and then use a freshly mixed borax standard solution to check that calibration (or just test some of the borax solution). Any significant variance in expected values will indicate either errors in calibration, errors in measurement, probe errors, or meter errors, or you may have degradation of the calibration standards at this point, what originally brought Craig to perform this test...
Plan on replacing the pH probes about every 18 to 24 months, although in rare instances the probes can last for as long as 3 to 4 years when immersed continuously in no-light environments and still give fairly good responses...
see:
http://thereeftank.com/forums/showthread.php?t=67560
Do the borax test and post your results for us, you can usually get this stuff at any Target in the cleaning goods section.
HTH
