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[quote author=Mr. Ugly link=topic=2564.msg26649#msg26649 date=1194726309]
Gotta test the hobby kits against a known reference standard.
[/quote]

But if your color percaption is off, or you don't look at it right, no known reference will do you any good :)
 
Reference standard will clue you in on systematic errors in the test procedures.

Color perception problem probably can't be helped.

Might be able to help if someone's blue endpoint is not the same as what the manufacturer intended for blue endpoint.

Probably most people just use reference standard as a sanity check in case of really weird numbers.
 
Even if hobby kits are off, they can be precise, though not necessarily accurate. That's where the reference standard is useful.

Precision is more affected by the user. And that can be helped by good lab technique. The test kit indicators and reagents are basically the same as what people use in chem labs... old school, anyways.

When I was taking quantitative analysis, we had to be able to show 3 test runs with results agreeing to within .2%. I had no problem doing that with titrations. But it does rely on technique.

The labs were scheduled for 4 hours. I usually finished in an hour or so, then went to the student union to drink beer. Then I'd come back and help the cute girls who were getting +/- 20% results on their titrations.

Yeah, they only liked me for my mad burette skilz :D

Anyway, even student chemists ended up taking 4+ hours to get their results. So probably even harder for non-chemists.
 
Well to try to descientize what Norman said.

There are many places were error can be introduced.
First is error with the measuring instrument, if you have a rule that has 1mm accuracy you can't get any more accurate than that, in the same way you have a test kit that each drop = 1dkH of alkalinity you can't get any more accurate than that... by following the directions, however by doubling the volume you can effectively half the precision down to 0.5 dKh, however I'm unsure how this works for non-linear values like pH (or if it does)..

The next error is the error is the human error, how accurately are you measuring your vial to be at 5ml? Are you sure you're dropping a single drop and not touching the sides so you're prematurely "popping" the droplet that's forming? These sorts of errors are human errors, and often I call them "sloppy errors" because these are ones that can be fixed if you spend a little more time and effort in doing your measurements.

Ok so maybe that doesn't clear things up, but then again I teach the physics version of this rather than a chemical version, but I'm guessing the ideas are the same.
 
:lol: Sorry, I totally understood that part ;)

Anyway, even student chemists ended up taking 4+ hours to get their results. So probably even harder for non-chemists.
Click to expand...

What are you trying to say Norm, I'm no scientist?
Click to expand...

Make sense now :)
 
Well $35 for a 1 time test is a lot it will give you an idea if your testing is accurate if you make the assumption that they are good at what they do :)
 
[quote author=Thales link=topic=2564.msg26701#msg26701 date=1194805144]
I'm going to Hunters at noon - anyone wanna come with?

Yes this has nothing to do with water testing.
[/quote]

Shoot, I would but I couldn't make it up there in time :) I'll be up later today though.
 
[quote author=LeviTillie link=topic=2564.msg26702#msg26702 date=1194806322]
Well $35 for a 1 time test is a lot it will give you an idea if your testing is accurate if you make the assumption that they are good at what they do :)
[/quote]

There is a whole lot of discussion about AWT, and discussion with AWT by chemists that seem pretty satisfied with their methodology. There may be an issue with the Silica (seems worked out) and the P04 which is getting worked out (and determined if there is actually an issue).
:D
 
[quote author=LeviTillie link=topic=2564.msg26702#msg26702 date=1194806322]
Well $35 for a 1 time test is a lot it will give you an idea if your testing is accurate if you make the assumption that they are good at what they do :)
[/quote]

I agree, however I think if you do a day of testing everything you possibly can, then use that same water to send a sample could be quite beneficial, at the very least let you know if you're tests are still working.
 
Rich are you still using this service? If so are you still happy with the results? I am thinking of giving them a shot. I am growing tired of the mixed results I keep getting from different test kits.
 
Sadly, the results from AWT seem mixed as well. There do seem to be some questions about their methodology - specially regarding Ca. However, I think they are pretty close to what we are doing with hobby test kits.

I am prolly going to buy another 4 pack from them, even though I just ordered new mg, ca, kh and phosphate test kits for the house.
 
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