Acceptable daily alkalinity swing

[Obdoc63]

I’m dosing two part and using my Trident to test 6 times a day. Alkalinity is ranging between 8.45-8.72. I’m adjusting to try to make that more stable, but is it really necessary? Searched the forum for an answer to this question and didn’t find it. Maybe I missed it though.
thank you for your reply.
Tim

 

[Randy Holmes-Farley]

There's no good data that indicates exactly what levels of alk swing are Ok and what levels are not.

I think most people would say your alk movement (< 0.3 dKH) is fine. I'd personally make it a low priority "fix" to reduce it.

 

[Obdoc63]

There's no good data that indicates exactly what levels of alk swing are Ok and what levels are not.

I think most people would say your alk movement (< 0.3 dKH) is fine. I'd personally make it a low priority "fix" to reduce it.

Thank You!

 

[gbroadbridge]

I’m dosing two part and using my Trident to test 6 times a day. Alkalinity is ranging between 8.45-8.72. I’m adjusting to try to make that more stable, but is it really necessary? Searched the forum for an answer to this question and didn’t find it. Maybe I missed it though.
thank you for your reply.
Tim

View attachment 3129929

Your doing pretty well.

I've been fiddling for 12 months and this is the best I can get it.

 

[Randy Holmes-Farley]

Your doing pretty well.

I've been fiddling for 12 months and this is the best I can get it.

View attachment 3129943

I assume the pH column is not correct?

 

[gbroadbridge]

I assume the pH column is not correct?

The probe is calibrated at ph 4 and 7, but it does drift down over a couple of weeks and is due to be cleaned and recalibrated tomorrow.

Somehow the software still manages to correctly determine the titration endpoint - I guess by looking at the inflection point.

 

[gbroadbridge]

I assume the pH column is not correct?

After cleaning and recalibrating the pH probe after 9am this morning.



Th pH is pretty close now, but it doesn't really affect the Alkalinity result.
It (KH Keeper+) loses significant accuracy if I leave it more than about a month without pH calibration.

 

[Randy Holmes-Farley]

Curious that it drifts so fast.

 

[Coolcasino]

Shouldn't you be calibrating at 7 and 10?

 

[Coolcasino]

I have a worse swing than you my friend. I can't get it any flatter than that.

 

[zheka757]

wow is checking it this much really necessary? I check mine ones or twice a month, on a 460g system, calsium reactor doing all the hard work for me

 

[Coolcasino]

wow is checking it this much really necessary? I check mine ones or twice a month, on a 460g system, calsium reactor doing all the hard work for me

Well I have my trident checking this often as I do the controlled dosing based on those results. I was trying to flatten out the reading but I've been thinking of going to 4 times a day as I haven't had to adjust the amount it doses in a long time. Maybe as my corals grow and consumption goes up I might go back if I see that the controlled dosing isn't keeping up.

 

[cpschult]

wow is checking it this much really necessary? I check mine ones or twice a month, on a 460g system, calsium reactor doing all the hard work for me

Trident has to test daily. If they are testing like that they probably aren’t using a calcium reactor, probably two part controlled by apex/trident

 

[gbroadbridge]

Shouldn't you be calibrating at 7 and 10?

No.

The endpoint of an Alkalinity titration is around pH 4.5

 

[Coolcasino]

No.

The endpoint of an Alkalinity titration is around pH 4.5

Oh wow. All ph probes I've used have always been 7 and 10. Fresh water IIRC I use to used 4 and 7. You must be taking a different reading of something totally different or your PH is measured differently than what I'm use to. Learn something new everyday.

 

[Randy Holmes-Farley]

Oh wow. All ph probes I've used have always been 7 and 10. Fresh water IIRC I use to used 4 and 7. You must be taking a different reading of something totally different or your PH is measured differently than what I'm use to. Learn something new everyday.

There are pros and cons of many different ways of calibrating a pH probe.

Most often, it is desirable to have your desired point of measurement in between two or more calibration points.

If the probe is being used to measure alkalinity by titration, then the critical points are in the pH 4-5 range. In that test, one adds acid until the pH reaches the specific ph endpoint and from the amount of acid needed, you know the alkalinity. A normal alk kit does this, but uses a dye that changes color at the pH endpoint, instead of a pH meter.

This article has more:

A Comparison of pH Calibration Buffers by Randy Holmes-Farley - Reefkeeping.com

How to Calibrate and Use a pH Meter

The most important aspect of using a pH meter is correctly calibrating it. Each meter will have a slightly different method of calibration. A number of general rules are very useful, however:

1. Any analytical method, including pH measurement, is best calibrated with quality standards that span the range expected to be measured. Most aquarists calibrate pH meters using two solutions of known pH. A meter that allows only one calibration point is a very poor choice. Using more is fine if the meter allows more than two. When using two solutions to calibrate a pH electrode for use in a marine aquarium, one calibration point should optimally be below 8.0 (typically 7) and one should be above 8.5 (typically 10, but 9 is also sometimes used). When measuring pH in something other than aquarium water, there may be special tricks to use which are detailed below.

Using pH 4 and 7 is often done, but can be a less optimal choice because the range expected to be measured for reef aquarium water (about pH 7.8 - 8.6) is outside of this calibration range. In some cases the error is small enough that this is acceptable; while in others, it may be a problem.

The tables below show the maximum errors that are attained from various errors in the standard buffer solutions themselves (with problems with the standards being the only source of error considered; in reality, there can be additional errors in real measurements). These tables were obtained by simply looking at how much the calibration solutions might vary (first column), then seeing by how much the actual measured value can be off if both standards vary to the stated maximum error and in directions that result in the maximum measurement error (which turns out to be varying in opposite directions when using pH 4 and 7, and varying in the same direction when using pH 7 and 10 standards).

It is clear that with similar errors in the standard solutions, the errors in the measurements at pH 8-10 are smaller when calibrating at pH 7 and 10 than at pH 4 and 7. Whether these differences are important depends on the application and expectations of the aquarist.

Additionally, when measuring pH in a fluid of a lower pH (such as inside a CaCO3/CO2 reactor), calibrating at pH 4 and 7 is more sensible than calibrating at pH 7 and 10.
2. Make sure the calibration standards are either new or at least adequate for the purpose. To be sure, use one of the brands recommended in this article.

I have several bottles of pH fluid that I have been using for years. Occasionally, I use a fresh bottle or packet to calibrate my meter. At that time I check the pH values of all of these older bottles, and note the pH on the bottle. I can then use that bottle for future pH calibrations BECAUSE my meter allows me to calibrate with standards at any pH (such as pH 7.03 and 8.85). If the meter does not allow the input of the pH values that precisely, then it is not possible to use this trick.

3. Rinse the pH electrode in pure fresh water before putting it into any calibration standard, and between each standard. Also, be careful to not transfer anything except a trace of purified water into the calibrations standards. Even tap water, when transferred into a calibration standard, can impact the pH.

4. It takes some time for a pH meter to get a correct reading. So let the meter equilibrate to each standard long enough that the value stabilizes (say, holding within +/- 0.02 pH unit for 30 seconds or longer). Some meters beep or otherwise indicate when they are suitably equilibrated.

5. Stirring the solution can help the pH probe equilibrate to the solution, but it also encourages CO2 to enter the fluid. This CO2 can lower the pH of high pH standards, such as pH 8 and greater. I stir mine for about 30 seconds (often with the pH probe itself, though I've also broken them this way) and then let it sit to get a reading.

6. The temperature of the standards is important for two reasons. One is that temperature changes actually change the standards' pH. The other is that the pH electrodes change their response as a function of temperature (described above). The change in standard solution pH as a function of temperature cannot be automatically adjusted for by inputting temperature into the meter, or via its ATC. It is an attribute of the exact chemistry of the buffer used. Some have pH that rises as temperature rises, and some fall as temperature rises. Others rise with temperature in some temperature ranges and fall with temperature in other temperature ranges. Aquarists should be aware of the exact pH at the temperature being used for calibration. Buffers will often have such pH values as a function of temperature printed on the bottle. For example, a standard phosphate buffer has a pH of 7.000 at 25ºC, but 7.04 at 15ºC (a small difference). At the same time, a carbonate buffer with a pH of 10.01 at 25ºC has a pH of 10.12 at 15ºC (a larger difference).

7. After calibrating the meter, go back and make sure that it reads the calibrating solutions correctly (to within whatever error is acceptable) to be sure that it was done correctly.

8. For certain kinds of pH measurements, direct comparison to a known standard may be more useful than using the absolute readings that the pH meter shows. For example, to assess the strength of limewater via pH, make a standard of known saturated limewater (from, for example, a teaspoon of calcium hydroxide in a cup of pure fresh water). That solution has a pH of about 12.45 at 25ºC, but regardless of what is measured, use the number as the standard and see how far off from actual limewater it is (if it is 0.1 pH unit lower, then the limewater is about 79% saturated; 0.2 pH units lower and it is 63% saturated; 0.3 pH units lower and it is about 50% saturated; 0.4 pH units lower and it is 40% saturated, etc.). In this case, exact temperature equivalence between the samples is important. A difference of only 3ºC means a pH difference of 0.1 pH unit for saturated limewater.

 

[Coolcasino]

So that's why I've never calibrated a pH probe for salt water with 4 and 7. I've never used one to measure alkalinity. Makes total sense now.

 

[spicymikey]

Regarding the alkalinity swing, I have had my alkalinity swing way more than that over the course of the day when making changes or adjustments. 8
5 to 10.0. Even though it wasn't intentional, and I wouldn't recommend doing this on purpose, there were no ill effects. There's really no need to worry about fluctuations like what you're describing. I also agree with some others who say you're probably testing way too much. Unless you're in the midst of making adjustments to your dosing and procedures, twice a day is more than enough. I have my Apex set up to test at the beginning of the day and the end of the day 6:00 a.m., 6:00 p.m. if you're really in a Groove and things are very stable then once a day is probably more than enough as well. Someone said they do it once a month. I would not recommend that. Alkalinity, calcium, and magnesium, are your three major elements and they are critical. You need to monitor them quite often . Your aquariums needs are going to change over time as your corals grow and you want to keep track of that drift to keep it in range.

As far as your pH probe. This probe is in the water 24/7 and is eventually going to develop organic slime, Etc on the bulb. You are going to want to clean it. Periodically. I take mine out and dip it in hydrogen peroxide for about 5 minutes once a week doing normal maintenance of my sump. As a matter of fact I do that with all the probes in the water. Having said that, realize these probes will "wear out". If you're having a hard time calibrating it, or keeping it calibrated, it might be time to replace it. Especially if it's more than a couple years old.

Hope that helps