A different approach to alkalinity testing... double check my "chemistry" please

[Reefinmike]

This sounds like a stupid question- Can I "test" alkalinity with a fixed amount of titrant? All I need is to know if it's below or at/above my desired setpoint.

I've owned an alkatronic for 10 months now and really do like the unit but I've been wanting to build my own tester for even longer. I'm pretty picky and a handful of factors really set this project into motion. According to Randy's article here http://www.reefedition.com/a-diy-alkalinity-test-by-randy-holmes-farley/ - " Alkalinity (in dKH) as a function of standard acid added to reach the endpoint in the given volume of aquarium water". I've extrapolated his 1 liter charts and found a nice balance using a 60ml sample with 1 part 0.1N acid diluted with 4 parts RODI for more precise measuring with doser pumps. As my alk demand sits now, a hourly test with a 60ml sample would be ideal to mitigate salinity rise from my dosing. I already have the apex programming figured out for automated dosing control based on the alkatronic reading and it's worked wonderfully for months. I have the entire testing procedure 99% figured out. I've beta tested programming through the entire testing procedure alongside my alkatronic dozens of times. All the fluid transfer is figured out. the bulk of the titration is good to go. Things just get really complicated when trying to "count" the final amount of titrant needed to reach 4.50 pH. It's possible but the apex's coding limitations won't provide me flexibility in easily adjusting my desired alk. More importantly, I couldn't really share all the programming with others... it would be too specific for my tank size, demand, desired alk, sample size and testing frequency.

Rather than measuring how much acid it takes for a set sample size to reach a pH of 4.50 or less- Why not just add a fixed amount of acid(representing my desired alk) with each test ? if pH is below 4.50 that means alkalinity is lower than I'd like. If above 4.50 then alkalinity is at or above my desired level. For example; I want to keep my alk around 9.30 and my demand averages 240ml a day- 10ml/hr average. I'll pull a fresh 60ml sample every hour, add 10.0ml of diluted acid and check the pH to dictate the next hours' dosing.
-If the pH is 4.50+ during low demand hours, dosing will fall back to 4 ml per hour. If that condition continues for three hours or longer, dosing will turn off completely. after 6 hours I will get an error alert.
-If the pH is below 4.50 during low demand hours, dosing will be 8ml per hour. if the condition continues for 3+ hours it will bump up to 12ml per hour. 6+ hours gets an alert
-If the pH is 4.50+ during peak demand hours, dosing will be 12ml per hour. if that condition continues for 3+ hours it will drop down to 8ml per hour. 6 hrs for an alert
-if the pH is below 4.50 during peak demand, dosing will be 16ml per hour. if that condition continues for 4+ hours I will get an alert
Of course this does NOT mean I'll set it up and just let it go. I will continue to test with salifert every 4-5 days to ensure nothing has drifted out of whack. I will check calibration of the pumps often as I do with my alkatronic and I will run the two testers side by side for a minimum of two weeks before taking the alkatronic offline.

This is feasible, correct?

 

[Shmollica]

@Randy Holmes-Farley writes some amazingly informative and accurate information, hopefully he gives you an answer! Ummm Henderson-Hasselbalch hahaha. I think you can do it this way; it’ll just take way longer and I don’t think you would get as close to your desired end point this way.

 

[taricha]

Rather than measuring how much acid it takes for a set sample size to reach a pH of 4.50 or less- Why not just add a fixed amount of acid(representing my desired alk) with each test ? if pH is below 4.50 that means alkalinity is lower than I'd like. If above 4.50 then alkalinity is at or above my desired level...

This is feasible, correct?

yes, it is that simple, and it'd be easily portable to any other system, by changing only the meq/L of acid added to represent the target alk.

Like you figured out, "is pH < or > 4.50" is a simpler coding question. And it'll tell you whether you need more or less alk added to hit your target. Most people do the same already just with less precision by assuming an alk level based on their overall tank pH, but I like your solution, one bulk addition of acid to a volume - check pH and know if your alk is above or below a target.
BTW, Do you have a stirring step, or does the dilution take care of that issue?
(I'll just point out, errors in coding the on and off conditions of alk additives do end up killing a lot of livestock in the hobby, but sounds like you have it pretty tightly controlled.)

 

[Reefinmike]

yes, it is that simple, and it'd be easily portable to any other system, by changing only the meq/L of acid added to represent the target alk.

Like you figured out, "is pH < or > 4.50" is a simpler coding question. And it'll tell you whether you need more or less alk added to hit your target. Most people do the same already just with less precision by assuming an alk level based on their overall tank pH, but I like your solution, one bulk addition of acid to a volume - check pH and know if your alk is above or below a target.
BTW, Do you have a stirring step, or does the dilution take care of that issue?
(I'll just point out, errors in coding the on and off conditions of alk additives do end up killing a lot of livestock in the hobby, but sounds like you have it pretty tightly controlled.)

Thanks for hearing me out! You wouldn’t believe the amount of redundancy I have on my system. I’m the kind of person that has all my dos power supplies on apex outlets for emergency shutoff based on pH, sump level etc. redundancy for outlets stuck in positions for too long etc etc. really at it’s heart, this is just a fun project to show whats possible. And itll be fun to watch Neptune and Focustronic’s eyes twitch. I pretty much perfected integrating the Alkatronic and dos pumps to do just what trident controlled dosing does... it’s actually better. https://www.reef2reef.com/threads/i...-staggered-chased-dosing.798993/#post-8508856

Yes, I have a stirring step. I have 8 or 9 virtual outputs labeled s1-s9. They’re just simple lines of OSC code that act as triggers to run dos profiles, my waste pump, stirrer etc. once the sample is taken, a mag stirrer turns on for 30 seconds while it takes a starting pH reading. This determines whether the next hour’s alk dosing will be lye or soda ash. I’ve been perfecting my chronically low pH this way for 5 months with impressive results. The next step triggers the acid dose(~45 seconds) and stays “on” with for 1:30 total. The mag stirrer stays on the entire duration.

I had coding figured out before where i could get a precise alk “number” with 0.05 dkh resolution. To make coding manageable it needed a 120ml sample which would’ve limited me to 12 daily tests. It would’ve worked but before going through with tying in the dosing control(lots more code), I thought this would be a better way. Yes it’s rudimentary but the simplicity allows for a smaller sample and more frequent checks on my dosing directive. It also allows for the system to be easily adapted for other people!

 

[Reefinmike]

@Randy Holmes-Farley writes some amazingly informative and accurate information, hopefully he gives you an answer! Ummm Henderson-Hasselbalch hahaha. I think you can do it this way; it’ll just take way longer and I don’t think you would get as close to your desired end point this way.

Actually, this method gives me a “reading” by the 6:30 minute mark. Once waste is emptied and the vial refilled with storage water, it’s about 09:15.

the titration method where the final 10% of the acid is “dripped” takes about 15:30 minutes. More pump noise tol

 

[Dan_P]

This sounds like a stupid question- Can I "test" alkalinity with a fixed amount of titrant? All I need is to know if it's below or at/above my desired setpoint.

I've owned an alkatronic for 10 months now and really do like the unit but I've been wanting to build my own tester for even longer. I'm pretty picky and a handful of factors really set this project into motion. According to Randy's article here http://www.reefedition.com/a-diy-alkalinity-test-by-randy-holmes-farley/ - " Alkalinity (in dKH) as a function of standard acid added to reach the endpoint in the given volume of aquarium water". I've extrapolated his 1 liter charts and found a nice balance using a 60ml sample with 1 part 0.1N acid diluted with 4 parts RODI for more precise measuring with doser pumps. As my alk demand sits now, a hourly test with a 60ml sample would be ideal to mitigate salinity rise from my dosing. I already have the apex programming figured out for automated dosing control based on the alkatronic reading and it's worked wonderfully for months. I have the entire testing procedure 99% figured out. I've beta tested programming through the entire testing procedure alongside my alkatronic dozens of times. All the fluid transfer is figured out. the bulk of the titration is good to go. Things just get really complicated when trying to "count" the final amount of titrant needed to reach 4.50 pH. It's possible but the apex's coding limitations won't provide me flexibility in easily adjusting my desired alk. More importantly, I couldn't really share all the programming with others... it would be too specific for my tank size, demand, desired alk, sample size and testing frequency.

Rather than measuring how much acid it takes for a set sample size to reach a pH of 4.50 or less- Why not just add a fixed amount of acid(representing my desired alk) with each test ? if pH is below 4.50 that means alkalinity is lower than I'd like. If above 4.50 then alkalinity is at or above my desired level. For example; I want to keep my alk around 9.30 and my demand averages 240ml a day- 10ml/hr average. I'll pull a fresh 60ml sample every hour, add 10.0ml of diluted acid and check the pH to dictate the next hours' dosing.
-If the pH is 4.50+ during low demand hours, dosing will fall back to 4 ml per hour. If that condition continues for three hours or longer, dosing will turn off completely. after 6 hours I will get an error alert.
-If the pH is below 4.50 during low demand hours, dosing will be 8ml per hour. if the condition continues for 3+ hours it will bump up to 12ml per hour. 6+ hours gets an alert
-If the pH is 4.50+ during peak demand hours, dosing will be 12ml per hour. if that condition continues for 3+ hours it will drop down to 8ml per hour. 6 hrs for an alert
-if the pH is below 4.50 during peak demand, dosing will be 16ml per hour. if that condition continues for 4+ hours I will get an alert
Of course this does NOT mean I'll set it up and just let it go. I will continue to test with salifert every 4-5 days to ensure nothing has drifted out of whack. I will check calibration of the pumps often as I do with my alkatronic and I will run the two testers side by side for a minimum of two weeks before taking the alkatronic offline.

This is feasible, correct?

I think the Hanna alkalinity checker works this way. A dose of acid and a color checker of the pH.