Measuring effluent dkh with Salifert

[ScottB]

I am down to my last box of Salifert Alkalinity while breaking in a new Calcium reactor. So I needed to dilute my sample to avoid wasting too much of the second reagent.

Effluent dkh calculation -- can someone check me out on this Salifert calculation?
a) 1 part effluent to 4 parts RODI
b) Four drops of reagent #1
c) 1.3 ml of reagent #2 to get the color change
d) Therefore, 15.7 + 4.5 = 20.2 diluted
e) 20.2 X 4 = 80.8 dkh undiluted

Am I thinking about this the right way?

This picture will help you figure out where I got the 15.7 and 4.5 numbers from.

 

[Randy Holmes-Farley]

You multiply by 5 (the volume of the diluent plus the sample divided by the sample volume), not 4, so you have 101 dKH.

That seems quite high.

 

[ScottB]

You multiply by 5 (the volume of the diluent plus the sample divided by the sample volume), not 4, so you have 101 dKH.

That seems quite high.

Thank you Randy. I will start another pot of coffee. The first was obviously too diluted.

My real life calcium reactor experience is counted in hours not years (so please forgive the noob question) but isn't this a crazy high number? I commonly read about others running 25, 45 dkh effluent.

 

[Randy Holmes-Farley]

Thank you Randy. I will start another pot of coffee. The first was obviously too diluted.

My real life calcium reactor experience is counted in hours not years (so please forgive the noob question) but isn't this a crazy high number? I commonly read about others running 25, 45 dkh effluent.

Yes, it seems very high to me as well.

Did you forget to dilute it? lol

 

[JimWelsh]

a) 1 part effluent to 4 parts RODI

You don't say how big those parts are. What was the total initial volume of diluted sample you took? Also, what color did you use as the endpoint? Please see the endpoint color I suggest here: https://www.reef2reef.com/threads/alkalinity-titration-endpoint-ph-salifert-endpoint-color.543556/

 

[Randy Holmes-Farley]

You don't say how big those parts are.

I hope that isn't the explanation. lol

 

[ScottB]

You don't say how big those parts are. What was the total initial volume of diluted sample you took? Also, what color did you use as the endpoint? Please see the endpoint color I suggest here: https://www.reef2reef.com/threads/alkalinity-titration-endpoint-ph-salifert-endpoint-color.543556/

Sample sizes were in milliliters. Interesting point about the color. I drip in to full pink typically which is several degrees different than lavender. Would account for SOME of the testing error. I have a (probably expired) Red Sea alk test kit somewhere and might try that.

 

[JimWelsh]

Sample sizes were in milliliters.

My Salifert alk kit says to use 4 mL of sample. So, if you took 1 mL effluent, you would multiply your result by 4, regardless of how much RODI you used to dilute it. Your original value of 80.8, after overshooting the endpoint, was apparently correct.

 

[Randy Holmes-Farley]

My Salifert alk kit says to use 4 mL of sample. So, if you took 1 mL effluent, you would multiply your result by 4, regardless of how much RODI you used to dilute it. Your original value of 80.8, after overshooting the endpoint, was apparently correct.

Did you do that, Scott? I presumed you used the right volume of the already diluted sample.

 

[ScottB]

Let me condition my 21:30 response by saying my kids just finished their respective college's academic commitments some few hours ago for graduation. Not that there will be a graduation, but the work is done. I have been trying to keep up with their beverage consumption since and it would seem my tolerance now is not quite what is was when I was their age.

To answer you @Randy Holmes-Farley directly -- even when sober I did not know the "right volume" and just worked with intuition. Kind of a visual thinker so the math I opened with just made sense. 1:4 test, so multiply result by 4.

I certainly used 1ml effluent and mixed it with 4 ml of RODI. And it required 1.3ml od #2 reagent to get solid pink.

I dug up a Red Sea ALK kit (before beverages). I did a 50/50 dilution and came back with effluent of 82 dkh. Of course another crap disclaimer: this kit expired in November 2019.

I really appreciate you both chipping in here. I wouldn't keep bothering you if I had my own convictions. Or if my effluent measures seemed conventional. But neither is presently true.

 

[JimWelsh]

I certainly used 1ml effluent and mixed it with 4 ml of RODI. And it required 1.3ml od #2 reagent to get solid pink.

Then, assuming your Salifert kit's instructions call for 4 mL of sample water, I stand by the "multiply by 4" answer above of 80.8 dKH. The amount of RODI you used is irrelevant; it's just "filler" in the analysis. What matters is that you only used 1/4 the amount of sample required (1 mL of effluent), so you multiply your result by 4.

EDIT: The fact that the Red Sea came in at basically the exact same number is a good confirmation of the result.

 

[ScottB]

Then, assuming your Salifert kit's instructions call for 4 mL of sample water, I stand by the "multiply by 4" answer above of 80.8 dKH. The amount of RODI you used is irrelevant; it's just "filler" in the analysis. What matters is that you only used 1/4 the amount of sample required (1 mL of effluent), so you multiply your result by 4.

EDIT: The fact that the Red Sea came in at basically the exact same number is a good confirmation of the result.

Yes, it calls for 4 ml sample then 4 drops of agent #1. Then drops of #2 until color change.

So I would NOT adjust the number of reagent #1 drops, correct?

 

[JimWelsh]

So I would NOT adjust the number of reagent #1 drops, correct?

No, that doesn't really matter at all, as long as you can see the color well. Which should be no issue with the volumes you are working with. Maybe add 1 additional drop, since both the RODI and the amount of reagent used makes the total volume at the endpoint a bit more than it usually would be. But, again, as long as you can see the color OK, then everything's good.

 

[Randy Holmes-Farley]

I agree with Jim's statement. I misunderstood what you did.

I assumed you used the correct (Salifert directions) amount of fluid for the alk test, but instead, it sounds like you used 5 mL for the alk test instead of the called for 4 mL.

 

[piranhaman00]

What I would do is take 10mL of effluent and mix it with 90mL of RODI. Use a graduated cylinder you can find on amazon. This is then your "tank sample". The greater volume you use for your dilution, the less error becomes an issue. Using 1mL into 4mL for a 1/5 will work but error becomes much more problematic.

Run the salifert test following the directions. Use 4mLs of "tank sample", and follow the rest of the directions.

If your effluent is really that high, this dilution will encompass it and you will not be wasting reagent. Whatever dKH you get, multiply by 10.

 

[Shinister]

That looks really complicated! I've been using this method. I cant remember where I got it from.

- Use 2ml of effluent
- Add 1 drop of dkh 1 and swirl
- Draw out 1ml of dkh 2 and start adding slowly until color change (if no color change, draw out another 1ml and continue dropping until color change)
- Add up total ml of dkh 2 used and multiply by 32

Am I doing it right?