Different FC results with new R0871 dropper.. smaller drops?


Apr 4, 2019
Houston, TX
First time changing to a new bottle of R0871 tonight and getting different FC results... not sure if this is normal and I should just trust the new and carry-on, or do some more troubleshooting to figure out the discrepancy and be confident with the new result? The older bottle is about 5months old (original t-100) newer bottle is 1mo old (T-100 refill).

todays results:
10ml FC test old- 11.5
10ml FC retest old -11

10ml FC test new -15
25ml FC test new - 15.4

Other results
CC - 0.5
ph - 7.9
TA- 70
CH - 200*
CYA - 50
Temp - 55F
CSI: -0.24

*Sidenote - i hadn‘t added more CH because CSI was manageable during the summer, but with lower temps now I think I’m going to need to so I can manage ph between 7.6-8... thoughts?

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Just to clarify .....I wondered if out of the two "old" test numbers at the top, which both say 10ML, was the first/top 0 ML and the 2nd one was actually 25 ML? To match the format as the new test numbers? You do show "re-test", so perhaps not, but figured I should ask.

By any chance did you try wiping the tip of the NEW bottles after each drop? Just in case they are harboring any static electricity? It has happened before, typically with other reagents when new, but when it does happen it can result in smaller drops.
  • Like
Reactions: wireform


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
I think the results are close enough not to worry about it. Nothing in pool water chemistry requires a very precise measurement.


Apr 4, 2019
Houston, TX
I had tested the old twice at 10ml, Only did 25ml with the new one.

Thanks for the suggestion! Didn’t try wiping the tip of the new one on prior tests. I just retested 10ml wiping the tip and got 13 With the new, and retested the old again And got 12. I think that’s within reason, so I’ll keep wiping the new one for awhile till the bottle settles in.
  • Like
Reactions: Texas Splash