One night I was getting frustrated because it seemed my results were off with the FAS-DPD, so I tested 3 times in a row, each a fresh pool sample and got 3 wildly different results.
So I bagged it and just walked away frustrated, questioning everything and decided not to worry about it. After that, it has all been fine. Why did that happen? Probably psychological, effecting the physiological aspect of the test. Got myself worried about it and thus it affected my agitation performance with the cylinder and screwed up my count.
Ever since then, I think it has gone rather well. I don't go quite so high speed with the drops, such that my counting isn't behind the actual number, IE. buffering visually in memory and counting that to keep up. I try to keep them at a speed I can actually count with them instead of racing to keep up, it's still about 1 per second though, as recommended with high FC.
Also, I don't OCD anymore over whether it's right on the 10ml mark, I just get it hairline close, under or over and if it gets right on the line. WOHOOO!!
As I slosh some out anyway when I'm swirling, so who cares!
Not sure how much that affects it once the DPD powder is added, it's only while titrating, but it is what it is. I'll have a speed stir soon anyway.
The endpoint can be a bit of a bugger, as sometimes I'm certain that even though that water is clear and not tinted clearly pink overall, that it's still got just a teeny, tiny little bit of rosy color to it. Almost like the cylinder itself is ever so slightly tinted, just enough that it tints the water.
So I see this by putting it in the light at different angles, I then place another drop, swirl it for a few seconds, then check again. Seems to be totally clear now, no phantom tint anymore.
But then I doubt myself, was there really one there before, or not, was it so slight, which it was, that the A>B comparison didn't occur fast enough for me to be certain? I don't know. *hrumpf*
For daily use, big whoop! Sure, it'd be nice to be more precise, but whatever, not exactly a big deal for CL dosing.
But for shocking, YEAH!! Big DEAL!! 0.5ppm can mean the difference between passing and failing.
Anyway, sorry for rambling, hope that gives some ideas, or sparks something, what have you.
TTFN!