DIY Alk test discussion thread

Randy Holmes-Farley · Jan 5, 2015

In case anyone wants to discuss the DIY alkalinity test that I recently published, I've started this thread.

Here's the article:

A DIY Alkalinity Test: By Randy Holmes-Farley - REEFEDITION

Happy Reefing!

UK_Pete · Jan 5, 2015

I havent had a chance to read the whole article properly but I'm really excited about this one personally, and will definitely be moving to this technique. Is it right to say that this will be much more accurate than a normal test kit, especially since you can use larger volumes to reduce titration errors, and because the color change method is much more subjective and can depend on the light (IE natural vs artificial etc)? I find interpreting my alk tests quite tricky because the color change starts and end points are about 1.5 dkh apart and I never really know if I have an accurate reading absolutely, or even relatively from the last time I did it. Thanks for the article Randy and I am sure this one will be a long time favourite with very many people like the 2 part articles you have done.

Cory · Jan 5, 2015

Hey Randy. Seems like a good article! Haven't had the chance to read it all yet. But my first concern was if I could use the ph meter of my neptune apex?

Randy Holmes-Farley · Jan 5, 2015

Thanks, guys.

You can use any pH meter that is calibrated.

dallasg · Jan 5, 2015

This is awesome, I am going to try this this week.
I use HCL acid for my pool, I will check the strength tomorrow

JimWelsh · Jan 5, 2015

Regardless of the percentage of HCl shown on your jug of swimming pool acid, its true concentration may vary significantly. It will probably be around 10N. You'd have to standardize it (after dilution, of course), e.g, by using a carefully made Na2CO3 primary standard and phenolphthlaein indicator.

UK_Pete · Jan 6, 2015

Jim - Or, I guess, the same pH probe and Na2CO3? I mean from what I can see, you only need one single calibrated thing, baked sodium bicarb would see to be one option, and the easiest for reefers who already have it, but once you have calibrated your acid, youre good to go for a long time.

Randy Holmes-Farley · Jan 6, 2015

I probably wouldn't use baked baking soda as a standard since it is hard to know for sure it is fully in the carbonate form. Ordinary baking soda might be a better bet for that, although I've not done it.

UK_Pete · Jan 6, 2015

Oh right. What about calcium hydroxide, I don't think thats too deliquescent is it? So titrate against an accurately weighed quantity of kalk powder to determine acid strength?

Randy Holmes-Farley · Jan 6, 2015

Assuming it is dry and hadn't been allowed to react with atmospheric CO2.

UK_Pete · Jan 6, 2015

Oh yes I see why. Apart from getting lag grade acids, what would your best diy way be of calibrating the acid?

Randy Holmes-Farley · Jan 6, 2015

Well, a high quality base. If you can get some pure lye (NaOH), that might be good. You can bake the heck out of it to drive off any moisture and possibly drive off any CO2.

UK_Pete · Jan 7, 2015

Sounds good thats something many of us probably already have too, thanks Randy.

dallasg · Jan 7, 2015

what would be the best off the shelve acid, that is easily accessible?
is it something i could get a chemical company to make for me

Randy Holmes-Farley · Jan 7, 2015

I suggested 0.1 N HCl (hydrochloric acid). Most chemical supply companies should already have it and sell it.

0.1 N H2SO4 (sulfuric acid) is equally suitable.

dallasg · Jan 7, 2015

thanks

Randy Holmes-Farley · Jan 7, 2015

You're welcome.

Let us know what you can find.

DFW · Jan 7, 2015

Randy Holmes-Farley said:
You're welcome.

Let us know what you can find.

Randy, thank you for your hard work on this! I do not think that I will be able, however, to make use of it.

I have a question. Could I make a gallon solution of Randy's Alkalinity #1 recipe mixed in ro di water at, for example, 10 dKH, and then just compare my store bought test kit to that as a check on how far it is off? By using the Reef Chemistry Calculator FV[FONT=Impact, Arial, Helvetica, sans-seriff] Â©[/FONT] By:JDieck I am showing to add 7.1 ml to that gallon of water to get 10 dKH. I don't expect that this is real accurate like your test given here, but might it get me a little closer than what I might be just using this store bought test? I could just adjust the test kit reading by however much I need to based on the test of the solution. Thank you! David

Randy Holmes-Farley · Jan 7, 2015

DFW said:
Randy, thank you for your hard work on this! I do not think that I will be able, however, to make use of it.

I have a question. Could I make a gallon solution of Randy's Alkalinity #1 recipe mixed in ro di water at, for example, 10 dKH, and then just compare my store bought test kit to that as a check on how far it is off? By using the Reef Chemistry Calculator FV Â© By:JDieck I am showing to add 7.1 ml to that gallon of water to get 10 dKH. I don't expect that this is real accurate like your test given here, but might it get me a little closer than what I might be just using this store bought test? I could just adjust the test kit reading by however much I need to based on the test of the solution. Thank you! David

You cannot use it because you don't have a pH meter?

My concern with what you suggest is that there will be a fair amount of uncertainty in exactly what the alkalinity is for such a solution because of the many measurements involved to get there (weight of baking soda, uncertainty of the mass/volume ratio if measuring by volume, volume of the water,a dn then the volume of the water for each step in the dilution).

If you don't have a pH meter, but just want a comparison, a standard base might be a better bet. 0.1 N NaOH is 100 meq/L (280 dKH). 0.01 N is 28 dKH. If you can buy the 0.01 N and dilute by a factor of 2, you have a 14 dKH standard.

DFW · Jan 7, 2015

Randy Holmes-Farley said:
You cannot use it because you don't have a pH meter?

My concern with what you suggest is that there will be a fair amount of uncertainty in exactly what the alkalinity is for such a solution because of the many measurements involved to get there (weight of baking soda, uncertainty of the mass/volume ratio if measuring by volume, volume of the water,a dn then the volume of the water for each step in the dilution).

If you don't have a pH meter, but just want a comparison, a standard base might be a better bet. 0.1 N NaOH is 100 meq/L (280 dKH). 0.01 N is 28 dKH. If you can buy the 0.01 N and dilute by a factor of 2, you have a 14 dKH standard.

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