Bad Reagent Read more or less FC?

[dailo]

I started SLAM a few days ago, but because I was low on R0871 I was just doing 5mL samples as I saw suggested in a few other threads. Maybe I didn't do it right, but looks like the results may have been wrong or the reagent is bad. The bottle from the TFT kit didn't have an expiration date, but I purchased it about 10 months ago so should still be good. Last few days I have been using the old bottle to try to keep my FC at 20. For the OCLT I wanted to use a 10mL sample and the new bottle came today (expires 6/23) so I did that but the test only came back with 12 FC. I did a 5mL sample to compare with the old bottle and that came back at 19 which is what I expected. A 5 mL sample with the new bottle came back with 16 so I wasn't really sure what number to believe. Put in another gallon of chlorine and did another 10 mL test which came back at 16, which according to the calculator is about right. I assume at this point I just have to stick with 10mL tests and trust the results from the new bottle. Hoping I pass OCLT and just leave it be, but seem like I may not have been at SLAM level this whole time. Also, would bad R0871 impact the CC test? Only reason why I did SLAM was because CC was 2 even though water was clear, but maybe the test was just off.

CYA 50
pH 7.3
TA 110
FC 16
CC 0

 

[Texas Splash]

As you've noted, the 5 ml sample is sometimes used when we're in a pinch and need a ballpark method to maintain FC when we're almost out of powder, but it's by no means as accurate as the 10ML. Very tough to be precise with such a small sample. I think looking forward with your 10 ml samples is best. It would not surprise me that your CC readings were also a bit off, but hopefully now you're back on track with the new powder.

 

[duraleigh]

The best thing about the FAS/DPD test is it's accuracy and precision. When you decide to cut back to a 5 ml sample, you give up those attributes.

 

[dailo]

Thank you. Going to wait for my FC to drop so I can see if I can do a 10mL sample with the old bottle to compare. Passed OCLT so looks like I am out of the woods for now, although did have 0.5 CC but FC remained at 16.