DIY Alk test discussion thread

cope413 · Jan 7, 2015

Would this work?

Hydrochloric / Muriatic acid, 950 ml [hydroc] | DudaDiesel Biodiesel Supplies

If so, what's the dilution necessary to get to .1 N?

Randy Holmes-Farley · Jan 7, 2015

DFW said:
Thank you for your prompt reply!

I cannot use it because I have no meter, and the whole thing is more than what I want to get involved in.

I am not sure that I can obtain that chemical. I tried to get some lye one time from an online candle making supply company, and they would not let me have it for some reason. To get a "0.01 N solution" sounds even more difficult. I found a company that sells the measured amount of lye - 0.40 grams - that one would make a liter of 0.01 N solution, but it looks like they will put me through lots of questions before they sell it to me. Could I perhaps make such a solution from some household product? Thank you again! David

It would be easier to buy from a place like this, if they let you:

Sodium Hydroxide 0.01N | Qorpak

or

Qorpak - Q00242-1 - Sodium Hydroxide 0.01N

or

Hach Sodium Hydroxide Standard Solution, 0.01 N, 100 mL # 67132 - Careforde Scientific Supply

LABCHEM CHEMICAL NAOH 0.01 NORMAL 1 LITER - Standards and Solutions - 8WCK8|LC242002 - Grainger Industrial Supply

Here's 1 N from ebay:

Sodium Hydroxide 1 0 Normal 500ml Poly Bottle Reagent | eBay

cope413 · Jan 7, 2015

Perfect, I've got a grainger account already. That'll do just fine.

Also, out of curiosity, what is your pH meter accuracy? I'm guessing it's much better than my .2, but I'm just wondering how much a +/- .2 could possibly swing the reading on alk.

Randy Holmes-Farley · Jan 7, 2015

Oops, that is for DFW who doesn't have a pH meter and is just looking for an alk standard.

But I expect Grainger also has acid standards. :)

cope413 · Jan 7, 2015

i just noticed that. I found the acid.

Thanks a lot. I just used my last of red sea alk reagent, and this seems much more fun, and cost effective.

cope413 · Jan 7, 2015

Here's the acid (sulfuric) on grainger - for those interested

http://www.grainger.com/product/LABCHEM-Sulfuric-Acid-WP94358/_/N-kr5/Ntt-acid?nls=0&sst=subset&ts_optout=true&s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/5CVU3_AS01?$smthumb$#nav=%2Fproduct%2FLABCHEM-Sulfuric-Acid-WP94358%2F_%2FN-kr5Z1z0hi15Z1z0o7k6%2FNtt-acid%3FR%3D9PYM9%26_%3D1420663033572%26nls%3D0%26picUrl%3D%252F%252Fstatic.grainger.com%252Frp%252Fs%252Fis%252Fimage%252FGrainger%252F5CVU3_AS01%253F%2524smthumb%2524%26s_pp%3Dfalse%26sst%3Dsubset%26ts_optout%3Dtrue

Randy Holmes-Farley · Jan 7, 2015

cope413 said:
Also, out of curiosity, what is your pH meter accuracy? I'm guessing it's much better than my .2, but I'm just wondering how much a +/- .2 could possibly swing the reading on alk.

My pH meter reads to +/- 0.001 pH unit, but I know I cannot calibrate it that accurately.

This graph from the article shows how much you would be off if the pH meter read too high or too low:

if you look at the y-axis and imagine a horizontal line across at pH 4.5, where it intersects the black line gives you the alkalinity (in meq/L; 1 meq/L = 2.8 dKH).

Then imagine a line across at, say 4.3 or 4.7, and that gives you the error based on pH uncertainty of +/- 0.2 pH units. It is not very much, but I've not done it to see the exact number.

DFW · Jan 7, 2015

Randy Holmes-Farley said:
It would be easier to buy from a place like this, if they let you:

Sodium Hydroxide 0.01N | Qorpak

or

Qorpak - Q00242-1 - Sodium Hydroxide 0.01N

or

Hach Sodium Hydroxide Standard Solution, 0.01 N, 100 mL # 67132 - Careforde Scientific Supply

LABCHEM CHEMICAL NAOH 0.01 NORMAL 1 LITER - Standards and Solutions - 8WCK8|LC242002 - Grainger Industrial Supply

Here's 1 N from ebay:

Sodium Hydroxide 1 0 Normal 500ml Poly Bottle Reagent | eBay

What a huge blessing you are!

So I take 1/2ml of the 1.0 Normal NaOH and place it in 1 liter of distilled water to get a 14 dKH comparison solution? Is that right? (If I am hijacking this thread then please erase all of my comments, hopefully after you answer this one!:party:)

Randy Holmes-Farley · Jan 7, 2015

DFW said:
What a huge blessing you are!

So I take 1/2ml of the 1.0 Normal NaOH and place it in 1 liter of distilled water to get a 14 dKH comparison solution? Is that right? (If I am hijacking this thread then please erase all of my comments, hopefully after you answer this one!:party:)

5 mL of the 1.0 N NaOH and 995 mL of fresh DI water (giving 1 L total) gives 14 dKH. :)

DFW · Jan 7, 2015

Randy Holmes-Farley said:
5 mL of the 1.0 N NaOH and 995 mL of fresh DI water (giving 1 L total) gives 14 dKH. :)

How much do I owe you? I feel like I should be paying you for a subscription of some kind!

With this I can "calibrate" each test kit when I get it.

Randy Holmes-Farley · Jan 7, 2015

DFW said:
How much do I owe you? I feel like I should be paying you for a subscription of some kind!

With this I can "calibrate" each test kit when I get it.

Just let us know what you find. :)

UK_Pete · Jan 8, 2015

Hi Randy,

Getting back to the pH probe alk test, I've noticed sometimes when I use my probe in a small beaker with a magnetic stirrer the pH reading sometimes is pretty unstable and I need to lift the beaker off to stop the magnet to get a reading. Is this a normal problem or is it likely to be something to do with a cheap probe or something like that? I want to use the stirrer to do the alk test because it is much faster to mix the acid with the sample but this problem gets in the way.

Thanks, Pete

Randy Holmes-Farley · Jan 8, 2015

That isn't always a problem as that is the way most folks in labs use them, but I can imagine that sometimes it causes electrical interference in the wiring coming to the probe. It should not impact the probe tip itself, I don't think.

What pH meter is it (not the probe)?

UK_Pete · Jan 8, 2015

Well its only a cheap hand held ph 600, so I guess its just not suitable for a mag stirrer if that dosent usually cause a problem. I do intend to get a better one anyway because this only reads to 0.1 pH resolution. Good to know that with a better probe / meter I can do this though because its far more convenient and quick to not have to swirl manually. Thanks Randy.

Rybren · Jan 8, 2015

Randy,

Great article. Thank you. Even though I only check my alk once or twice a year, I'll have to go out and buy myself a pH meter and some acid so I can try your method out.

I think that there is a typo in Step 4 of the article (in the formulas). It seems to me that the meq/L and dKH formulas are reversed: Shouldn't Formula 1 determine dKH and Formula 2 determine meq/L? The example seems to use Formula 1 to determine dKH.

Cheers

Randy Holmes-Farley · Jan 8, 2015

Rybren said:
Randy,

Great article. Thank you. Even though I only check my alk once or twice a year, I'll have to go out and buy myself a pH meter and some acid so I can try your method out.

I think that there is a typo in Step 4 of the article (in the formulas). It seems to me that the meq/L and dKH formulas are reversed: Shouldn't Formula 1 determine dKH and Formula 2 determine meq/L? The example seems to use Formula 1 to determine dKH.

Cheers

Thanks. Yes, that is a typo. I switched the order of them and didn't change everything correctly. I'll have that changed ASAP.

Randy Holmes-Farley · Jan 8, 2015

UK_Pete said:
Well its only a cheap hand held ph 600, so I guess its just not suitable for a mag stirrer if that dosent usually cause a problem. I do intend to get a better one anyway because this only reads to 0.1 pH resolution. Good to know that with a better probe / meter I can do this though because its far more convenient and quick to not have to swirl manually. Thanks Randy.

You're welcome.

Happy Reefing. :)