Experimental testing of Brightwell Boost pH +

[Dan_P]

How well do hobby alkalinity measurements detect the alkalinity increase from adding Boost pH+ to a saltwater aquarium? I compare the results of the Hanna Checker with the Red Sea and API titration methods.

Alkalinity in our aquarium water is usually determined by titration, the addition of acid to a sample of aquarium water containing an indicator until a change in color occurs at the endpoint. The amount of acid needed to cause the indicator to change color corresponds to the amount of alkalinity present in the sample.

The Hanna alkalinity Checker uses a somewhat different approach, adding a single dose of acid and measuring the resulting pH with a pH sensitive dye. The dye color intensity (absorbance measured at 606 nm) increases with increasing pH.

A higher alkalinity in the sample causes a higher pH in the reagent sample mixture. Alkalinity and color intensity are linearly related.

Methods Modification

API. This titration method adds acid in large steps, making the detection of small changes in alkalinity impossible. To correct this with a minimum amount of change to the API method, a back titration strategy was used. In this approach, one additional drop of the API reagent is added after the endpoint is reached. Then using a one mL syringe fitted with a tip, additional water sample is added drop wise to the over titrated sample until the endpoint color reappears. Multiplying the number of reagent drops (alkalinity) by 5 and dividing by the total volume of the sample, i.e. 5 mL plus the extra volume, gives the alkalinity of the sample with higher precision.

Hanna Checker. When I compared my Hanna Checker alkalinity measurements to the amount measured by titration, the Checker results were consistently higher (post #170). To correct the Checker readings, a calibration curve was generated with a sodium bicarbonate solution and titrated aquarium water. Note how well the Red Sea titration performs.

Measuring Alkalinity Change.

The alkalinity of a 500 mL sample aquarium water was determined by titration (see table, first entry in “Alkalinity Calc” column) and the three hobby kits. Then a sufficient amount of Boost pH+ (0.23 N, 230 meq/L) was added to increase the pH 0.3 units, followed by alkalinity measurements. A total of two Boost pH+ additions were made. Triplicate measurements were made with Red Sea and API, and one measurement with the Hanna Checker (precision is calculated) after each Boost pH+ addition. The calculated alkalinity of the solution is the sum of the initial alkalinity and the added Boost pH+ alkalinity. The results are summarized in the table below and the bar chart below the table provides a visual comparison.

I conclude that all methods detect an alkalinity increase when Boost pH+ is added to aquarium water and provide reasonably accurate measurements with decent precision. The API method might be improved by moving to a syringe titration because of variable drop size using the bottle and the high concentration of the reagent. In both titrations kits, the endpoint color was aggravatingly vague to my eye but with practice it would probably be very repeatable. The Hanna high reading is a mystery. I need to buy another lot of reagent and measure both the acid content and dye concentration to see if either or both are different than the lot of reagent I now have.

 

[taricha]

A higher alkalinity in the sample causes a higher pH in the reagent sample mixture. Alkalinity and color intensity are linearly related.

Methods Modification

That's still just wild to me that it works this way and you can get sample Alk + known acid -> pH -> pH indicator absorbance that is linear to the initial sample alkalinity.

When I compared my Hanna Checker alkalinity measurements to the amount measured by titration, the Checker results were consistently higher (post #170).

the offset is around +0.5dKH high uniformly. Which isn't too bad considering my API bottles and Red sea kits disagreed by over one dKH.

I remember the hanna Alk had an issue with the reagent working less well over time, and storing it in the fridge helped. Then they said they fixed it. I don't remember which way it drifted as it got old - to higher absorbance and Alk or lower.

 

[Dan_P]

That's still just wild to me that it works this way and you can get sample Alk + known acid -> pH -> pH indicator absorbance that is linear to the initial sample alkalinity.



the offset is around +0.5dKH high uniformly. Which isn't too bad considering my API bottles and Red sea kits disagreed by over one dKH.

I remember the hanna Alk had an issue with the reagent working less well over time, and storing it in the fridge helped. Then they said they fixed it. I don't remember which way it drifted as it got old - to higher absorbance and Alk or lower.

Me thinks evaporation was the issue with the Hanna reagent. Storing it cold reduced the evaporation rate.

If the solvent evaporates, acid concentration increases making it look like there is less alkalinity in the sample. If a volatile acid is used in the reagent, maybe it degasses faster than evaporation of solvent and alkalinity appears to be higher.

I crank down my reagent lid and it seems to be fine bottle to bottle for the same lot. Maybe I’m just luckty

 

[Randy Holmes-Farley]

I would be interesting to see the absorbance spectrum of old/aged Hanna reagent against new reagent. Many dyes will oxidize and that can change the spectrum, which would mess up an alk test like the Hanna.

 

[Dan_P]

I would be interesting to see the absorbance spectrum of old/aged Hanna reagent against new reagent. Many dyes will oxidize and that can change the spectrum, which would mess up an alk test like the Hanna.

Any ideas about “aging“ the dye under controlled conditions?

 

[Randy Holmes-Farley]

Any ideas about “aging“ the dye under controlled conditions?

I assume you do not have a controlled temp and humidity chamber, but that is how accelerated drug stability testing would be done, with specific times, temps and humidities being specified.

FDA goes into great detail here:

Expiration Dating and Stability Testing for Human Drug Products

Drugs

www.fda.gov

but a common one is 40 deg C at 75% RH. If a drug (in its normal bottle) is stable in that for 6 month, then companies can usually claim a 2 y shelf life without waiting 2 years to see.

In this cause, I think comparing old and new is a good first step.

 

[Dan_P]

I assume you do not have a controlled temp and humidity chamber, but that is how accelerated drug stability testing would be done, with specific times, temps and humidities being specified.

FDA goes into great detail here:

Expiration Dating and Stability Testing for Human Drug Products

Drugs

www.fda.gov

but a common one is 40 deg C at 75% RH. If a drug (in its normal bottle) is stable in that for 6 month, then companies can usually claim a 2 y shelf life without waiting 2 years to see.

In this cause, I think comparing old and new is a good first step.

Sounds reasonable.

I don’t have feel - completely in the dark actually- for how long folks take to use up an opened bottle. I suppose that I could open a new bottle, obtain the spectrum and take a measurement of tank water that has been titrated for alkalinity. Then close up the reagent bottle as usual, weigh it and repeat, collect Vis spectrum and alkalinity measurement reweigh bottle, every 1-2 months until I get bored or see a change, say a year?. Sound useful?

 

[Randy Holmes-Farley]

Then close up the reagent bottle as usual, weigh it and repeat, collect Vis spectrum and alkalinity measurement reweigh bottle, every 1-2 months until I get bored or see a change, say a year?. Sound useful?

Yes. The rate is likely to be temp dependent and may be dependent on the numbers of times per week it is opened (if O2 gets depleted inside the bottle). So keep track of both.

 

[Dan_P]

Yes. The rate is likely to be temp dependent and may be dependent on the numbers of times per week it is opened (if O2 gets depleted inside the bottle). So keep track of both.

Got it.

Since I will be using several mL of reagent for tests every month or so but only open the bottle once, I will open the bottle weekly but not take out reagent to keep the number of bottle openings equal to the number of tests in the bottle (25).

 

[A_Blind_Reefer]

I would be interesting to see the absorbance spectrum of old/aged Hanna reagent against new reagent. Many dyes will oxidize and that can change the spectrum, which would mess up an alk test like the Hanna.

It would help answer the observations many of us have noticed. Storing opened reagent in the fridge as @Lasse concluded has eliminated the roughly 1dkh difference I was noticing when switching from a two to three month old opened reagent to a fresh unopened one.

 

[Dan_P]

It would help answer the observations many of us have noticed. Storing opened reagent in the fridge as @Lasse concluded has eliminated the roughly 1dkh difference I was noticing when switching from a two to three month old opened reagent to a fresh unopened one.

I should see some sort of change in less than a year.

 

[A_Blind_Reefer]

I should see some sort of change in less than a year.

I would hope so! Ha. Otherwise it will become rather evident that I have mental issues! Well, more than I’m already aware of anyway

 

[rtparty]

I have a bottle of reagent that has to be over a year old at least. Maybe older. Never refrigerated and still reads the same. Let me pull it out of the cabinet and see when it “expired”

 

[Dan_P]

I have a bottle of reagent that has to be over a year old at least. Maybe older. Never refrigerated and still reads the same. Let me pull it out of the cabinet and see when it “expired”

Ditto here.

I had an opened bottle, at least two months old, and new bottle from the same lot, and obtained the same alkalinity reading with each bottle. It will be interesting to see what happens in the stability study.

 

[BeanAnimal]

What about using collapsing bottles to eliminate most of the trapped air.

Used them in the darkroom, as developer oxidizes quickly and is a PITA to make.

 

[Dan_P]

What about using collapsing bottles to eliminate most of the trapped air.

Used them in the darkroom, as developer oxidizes quickly and is a PITA to make.

Good idea. If there is a round testing, definitely would consider this as a control rather than filling the headspace with nitrogen.

 

[BeanAnimal]

Good idea. If there is a round testing, definitely would consider this as a control rather than filling the headspace with nitrogen.

Polyethylene collapse bags or amber iv bags would also work very well. I can no longer find 50ml and 100ml collapsible solution bottles.
I can’t find small bladder bottle in that size either.

 

[JackKent1]

You guys all did a great job!

I think we are all set now. I’ll send that last graph to Jack and will work on a summary post/ thread when I get a chance.

The Boost pH+ product looks to raise pH and alk just as one would expect if its only active ingredient was the hydroxide known from Brightwell to be in it. There’s no need to invoke or hypothesize any effects from proprietary ingredients.

As an aside, the expected pH boost from adding hydroxide (or carbonate) depends on both the starting alk and the starting pH. The effect is biggest at low starting alk and pH for reasons related to buffering detailed here:

Chemistry And The Aquarium: Boron In A Reef Tank

This article also discusses the sources and sinks for boron in reef tanks, and shows that while typical tanks may be slightly depleted in boron with respect to natural levels, most are not so significantly depleted that any correction is required. Nevertheless, how to test for and supplement...

reefs.com

Buffering capacity can be quantified using the buffer intensity, b, defined mathematically in a way that is easy to calculate, but that isn’t worth detailing here.2 The units of the buffering intensity can be expressed as meq/L or meq/L/pH unit (these are equivalent since pH is really a dimensionless parameter). Thinking about it as meq/L/pH unit makes it easier to understand that it is a measure of the amount of alkalinity (or acidity; either one measured as meq/L) that needs to be added to impact the pH up or down by one unit (though that is a substantial simplification).

In the case of normal seawater at pH 8.2, b = 0.19 meq/L/pH unit for the boric acid/borate system, and 0.63 meq/L/pH unit for the bicarbonate/carbonate system. These values are additive, and result in a total buffering of b = 0.82 meq/L/pH unit. Under these conditions, the boric acid/borate system provides about 23% of the total buffering, while the bicarbonate/carbonate system provides about 77%.

If the pH of normal seawater is raised to 8.5, the total buffering is b = 1.2 meq/L/pH unit, or about 40% greater than at pH 8.2 (because both systems are closer to the pKa). At this pH, the relative contribution of the two systems to the total capacity is only slightly different than at pH 8.2, with 20% from borate and 80% from carbonate.

If the pH of normal seawater is lowered to 7.8, the total buffering is b = 0.42 meq/L/pH unit, or about half that at pH 8.2 (because both systems are farther from the pKa). At this pH, the relative contribution of the two systems to the total capacity is also only slightly different than at pH 8.2, with 29% from borate and 71% from carbonate.

We have now completed our testing of Boost pH+ and have determined that it does, in fact, raise the alkalinity of an aquarium when used as directed on the bottle. We were wrong. We will be revising our labels and all advertising to reflect this.

I want to apologize for our error. We certainly did not intend to mislead anyone. Oddly, we had not had any compaints from users. I am also open to suggestions from forum members of other steps we should take to correct the error.

We did receive some criticism on the forum about our use of an API test kit for our initial testing after Randy's original posts. Although I have no problem with that test kit, other than the courseness of the results, increments of a whole dKH, it was the only test kit that I had on hand at the time, and the lead time to get reagents for our other kits was long, due to the Christmas holiday season.

As for all of our products, we are willing to replace or provide a replacement or a different product to any customer who has purchased Boost pH+ and is unhappy with the product. Additionally, I would like to offer to give a free sample of anything we make to any forum member that did the experiment to test Boost pH+, to help compensate for your costs. Just send me an email, to [email protected] with what you want and address information for shipping.

 

[Randy Holmes-Farley]

In terms of whether it is plausible to use up O2 in the head space above a bottle, here's how to think of it.

Suppose there is 500 mg of bromcresol green (mw = 698) in water in a 100 mL bottle (just wild guesses), with a head space of 10 mL.

If each dye molecule reacted with one O2 molecule then 0.5 g/698 g/mole = 0.00072 moles of O2 is consumed.

One mole of gas occupies ~22.4 L at room temp and pressure, so that is 16 mL of pure O2 or about 80 mL of normal air.

Thus it is possible that O2 may get depleted inside if oxidation is taking place without frequently opening it (preserving it).

That said, I have no idea if the 500 mg assumption is even remotely correct.

 

[Randy Holmes-Farley]

Bromcresol green also suffers UV and possibly even visible light degradation.

I wonder if that might even be partly why storing in a fridge helps: not just cold but dark.