DIY Alkalinity Monitor

[Borat]

i'm using 75ml as sample (100ml doesn't increase accuracy a lot, something like 0.05, but takes 15 minutes more to fill). but the acid is (i think) 0.02 when diluted

And how much acid was used, what DKH was calculted and what end PH was for one of recent tests?

 

[iLMaRiO]

7.2dkh , 9.6ml HCl , 7.67 pH

Hanna checker and tropic Marin kh pro, show 8.6. Elos test kit is 17 drops, so 8.5

 

[iLMaRiO]

Interesting.. maybe could you post one of your recent test figures:
- sample water volume
- added 0.1N acid volume
- end PH (is it 4.5?)

If you have it - full step-by-step sequence similar to :
Step: ACID: PH
0: 0.00 : 8.10
1 : 4.00 : 6.66
2 : 6.00 : 6.08
3 : 8.00 : 5.73
4 : 9.00 : 5.53
5 : 10.00 : 5.33
6 : 11.00 : 5.06
7 : 12.00 : 4.64
8 : 12.07 : 4.56
9 : 12.14 : 4.52
10 : 12.21 : 4.47
11 : 12.29 : 4.43
12 : 12.36 : 4.35

DKH: 8.62 (using 0.025N)

morning test:

7.66;0.00;0.00
5.45;8.00;5.97
5.15;9.00;6.72
4.48;10.00;7.47
4.43;10.05;7.50
4.34;10.10;7.54

PH ; ACID ; KH

 

[Borat]

morning test:

7.66;0.00;0.00
5.45;8.00;5.97
5.15;9.00;6.72
4.48;10.00;7.47
4.43;10.05;7.50
4.34;10.10;7.54

PH ; ACID ; KH

You are not doing a lot of steps - how long does it take between each step? I use relatively large number of steps - even though seemingly I can cut the time significantly by agressively moving towards 4.5-ish range. The reason I do it slowly - is that each step gives a chance to significant amount of stirring and time - allowing for alkalinity to react with acid..

Not sure if that could be the reason - but I would cut the amounts on each step by half (you will probably end up with 3x number of steps).

 

[iLMaRiO]

You are not doing a lot of steps - how long does it take between each step? I use relatively large number of steps - even though seemingly I can cut the time significantly by agressively moving towards 4.5-ish range. The reason I do it slowly - is that each step gives a chance to significant amount of stirring and time - allowing for alkalinity to react with acid..

Not sure if that could be the reason - but I would cut the amounts on each step by half (you will probably end up with 3x number of steps).

but on each step you are adding some dosing errors. 1 single dosage is much more accurate than 10 small dosages that's why im doing a huge initial step.

keep in mind that i stir during the reagent dosage plus 10 secs, so if the first step takes 5 minutes, the stirting is done for 5 minutes and 10 seconds.

stir time increase when dosage decrease. under ph 4.6 i stir for not less than 30 seconds (plus the dosage time)

this is the log from the nightly test (i've increased the steps). It took 57 minutes.

pH ; HCl; dKh
7.50;0.00;0.00
5.36;8.00;5.97
5.19;8.50;6.35
4.96;9.00;6.72
4.91;9.10;6.79
4.85;9.20;6.87
4.78;9.30;6.94
4.67;9.40;7.02
4.59;9.50;7.09
4.59;9.52;7.11
4.55;9.54;7.12
4.55;9.56;7.14
4.55;9.58;7.15
4.51;9.60;7.17
4.51;9.62;7.18
4.46;9.64;7.20
4.47;9.66;7.21
4.43;9.68;7.23
4.43;9.70;7.24
4.44;9.72;7.26
4.39;9.74;7.27

 

[iLMaRiO]

do you use Just the hose for the reagent or with some "tip" / "nozzle" to make the drops? because i've found that my drops arent perfect, most of the time one drop is 0.03ml, then some other are 0.04

 

[Borat]

do you use Just the hose for the reagent or with some "tip" / "nozzle" to make the drops? because i've found that my drops arent perfect, most of the time one drop is 0.03ml, then some other are 0.04

I use a plastic syringe tip. As for precision - no precision should be lost by splitting the dose, at least not if you use stepper motors and you are holding the torque on your pump..

Small amount of one-off precision loss is if you don't uses a thin tip at the end of acid tubing..

 

[Borat]

I must say you have a very low starting PH level! I had mine as low as 7.8, maybe 7.7 at some point in the past, but I have never seen 7.5 being the level in my tank...

 

[iLMaRiO]

at night is very low the pH.

and i don't have any tips at the end of the tuning, that could be the issue?

(yes, stepper motor pump, the kamoer orange with 6 wheels)

 

[Borat]

at night is very low the pH.

and i don't have any tips at the end of the tuning, that could be the issue?

(yes, stepper motor pump, the kamoer orange with 6 wheels)

Not really - that's imprecision probably equivalent to a couple of acid drops, but no-where near your 10% discrepancy to other tests. Maybe your acid is a bit more concentrated than you think, you only need 10% strength discrepancy to explain the difference...

Out of interest - when you send signal to acid pump, do you keep "EN" pin HIGH for the whole duration of the test?

 

[iLMaRiO]

no, i disable the motor, but i don't see any extra drop going out (or back)

yes, im almost sure it's an issue with my reagent, still not found a way to diluire It properly even using a precision scale (0.01g)

 

[iLMaRiO]

New test with enable pin always on for the full test. dkh 8.1. I'll wait for the automated test at 13:30 and at the same time i'll do a manual test with the hanna checker. Let's see if the values match.

(tested the reagent accuracy: asked for 2ml and dosed exactly 2ml), so, probably the reagent i'm mixing is not perfect (a molarity of 0.02 vs 0.025 is more or less 0.5dkh)

 

[Borat]

New test with enable pin always on for the full test. dkh 8.1. I'll wait for the automated test at 13:30 and at the same time i'll do a manual test with the hanna checker. Let's see if the values match.

(tested the reagent accuracy: asked for 2ml and dosed exactly 2ml), so, probably the reagent i'm mixing is not perfect (a molarity of 0.02 vs 0.025 is more or less 0.5dkh)

Glad you are getting sorted with your discrepancies! I doubt you will always be fully in line with other commercial tests, deviations of 0.3DKH to other tests are mainly explainable by the choice of endpoint PH (or choice of titrant colour: whether titrate to pink or to lavender (i.e. in-between being blue and pink) in the case of Salifert test).

 

[iLMaRiO]

Glad you are getting sorted with your discrepancies! I doubt you will always be fully in line with other commercial tests, deviations of 0.3DKH to other tests are mainly explainable by the choice of endpoint PH (or choice of titrant colour: whether titrate to pink or to lavender (i.e. in-between being blue and pink) in the case of Salifert test).

No, i'm not sure i've fix the discrepancies, i've tried without powering off the steppers, but i just did a single test (without the comparison) and dkh was much higher than the previous one. I'll do the comparison at 13:30

Yes, some discrepances are expected, but just a little, not 0.5/0.6 as minumum

 

[Borat]

No, i'm not sure i've fix the discrepancies, i've tried without powering off the steppers, but i just did a single test (without the comparison) and dkh was much higher than the previous one. I'll do the comparison at 13:30

Yes, some discrepances are expected, but just a little, not 0.5/0.6 as minumum

Where are you based? Mainland Europe?

 

[iLMaRiO]

Where are you based? Mainland Europe?

Italy

i've talked too early. latest test: 7.73, tropic marin 8.1, hanna 8.4. So, exactly as previously, 0.40 less.

 

[iLMaRiO]

test1: pH, HCl, dkh
6.93;0.00;0.00
6.29;3.00;2.24
5.83;6.00;4.48
5.80;6.50;4.85
5.66;7.00;5.23
5.65;7.50;5.60
5.60;8.00;5.97
5.45;8.50;6.35
5.39;9.00;6.72
5.19;9.50;7.09
5.10;10.00;7.47
4.85;10.50;7.84
4.76;10.60;7.91
4.71;10.70;7.99
4.65;10.80;8.06
4.64;10.90;8.14
4.53;11.00;8.21
4.54;11.05;8.25
4.52;11.10;8.29
4.48;11.15;8.33
4.45;11.20;8.36
4.41;11.25;8.40
4.38;11.30;8.44


test2, done immediatly after the first one
6.66;0.00;0.00
6.18;3.00;2.24
5.73;6.00;4.48
5.69;6.50;4.85
5.63;7.00;5.23
5.53;7.50;5.60
5.43;8.00;5.97
5.28;8.50;6.35
5.15;9.00;6.72
4.97;9.50;7.09
4.93;9.60;7.17
4.91;9.70;7.24
4.86;9.80;7.32
4.81;9.90;7.39
4.73;10.00;7.47
4.69;10.10;7.54
4.64;10.20;7.62
4.53;10.30;7.69
4.52;10.35;7.73
4.48;10.40;7.77
4.45;10.45;7.80
4.43;10.50;7.84
4.39;10.55;7.88

8.44 vs 7.88
honestly i don't see where the error is

 

[Borat]

test1: pH, HCl, dkh
6.93;0.00;0.00
6.29;3.00;2.24
5.83;6.00;4.48
5.80;6.50;4.85
5.66;7.00;5.23
5.65;7.50;5.60
5.60;8.00;5.97
5.45;8.50;6.35
5.39;9.00;6.72
5.19;9.50;7.09
5.10;10.00;7.47
4.85;10.50;7.84
4.76;10.60;7.91
4.71;10.70;7.99
4.65;10.80;8.06
4.64;10.90;8.14
4.53;11.00;8.21
4.54;11.05;8.25
4.52;11.10;8.29
4.48;11.15;8.33
4.45;11.20;8.36
4.41;11.25;8.40
4.38;11.30;8.44


test2, done immediatly after the first one
6.66;0.00;0.00
6.18;3.00;2.24
5.73;6.00;4.48
5.69;6.50;4.85
5.63;7.00;5.23
5.53;7.50;5.60
5.43;8.00;5.97
5.28;8.50;6.35
5.15;9.00;6.72
4.97;9.50;7.09
4.93;9.60;7.17
4.91;9.70;7.24
4.86;9.80;7.32
4.81;9.90;7.39
4.73;10.00;7.47
4.69;10.10;7.54
4.64;10.20;7.62
4.53;10.30;7.69
4.52;10.35;7.73
4.48;10.40;7.77
4.45;10.45;7.80
4.43;10.50;7.84
4.39;10.55;7.88

8.44 vs 7.88
honestly i don't see where the error is

Which voltage regulator are you using for your device?

Your starting PH seems wrong.. it is difficult to see how it can be 6.93 and it definitely can't be 6.66...

 

[iLMaRiO]

Which voltage regulator are you using for your device?

Your starting PH seems wrong.. it is difficult to see how it can be 6.93 and it definitely can't be 6.66...

AMS1117

oh, yes, i didnt notice the low starting pH, i have to check that

 

[Borat]

In terms of titration process - it's giving your relatively consistent results, i.e. your second test PH curve has a similar shape to first test PH curve but starts at a later PH point, it's just that in the second test you seem to have dumped 1.3ml of acid before the test began..

That's not to say 1.3ml is the only problem here - you first test also seem to have been affected by acid addition prior to test...