Water test kits and pH pens

[cdelucia]

I've got a complete Hagen test kit for fresh water which includes about nine tests (I don't use all of them). I test for Fe, NO3, PO4, pH, KH, and GH. I was just about to do a water change and decided to take my samples beforehand.

The tests are the test tube variety with the color charts for results and I was just wondering how long is the water good for testing? I took my samples, pust the plastic caps on the test tubes (loose caps - not tight mind you) and after all my cleaning, trimming, pruning, and water change I did the tests with the aforementioned samples. So, the water sat for about two hours. Am I messing up my results by waiting two hours? Like I said the caps are on and the test tubes are enclosed in the carrying case thingy.

Secondly, does anybody use a pH pen? Every now and then I'll find some on discount in a catalog and be tempted to pay upwards of $60 for one. Doesn't the electrode on the tip eventually need replacing? How much for the replacement? Some of them even test for conductivity and total dissolved solids. Um, why bother with the last two parameters? Is total dissolved solids the same as GH?

[benny]

Hmm... I don't recall seeing Hagen test kits here, perhaps that why you haven't got a response.

In most cases, the test kit only require a minute to two to show results. Certainly not two hours. Although I don't see how that will mess up the results.

Personally, I do use pH pens as well as pH controllers/meters. The probes on the pens are not replaceable, but they are usually good for up to 1000 applications. even if you test once a day, they are good for almost 3 years! But you have to store the pen properly.

Cheers,

p.s. I'm shifting this to equipment as it's about test kits and pH pens.

[cdelucia]

Okay.

I was referring to the amount of time the water sits out before I actually get around to testing it, period. I just wondered if the water's parameters could change if I leave it sitting out for two hours (albiet it's in a test tube with the cap on - again, a 'loose' cap)?

Hagen test kits are the test tube type with the color charts. Incidentally, I find the color charts hard to match. Basically I've observed you have two things to match: lightness and hue. And those two don't always go together. But then again, what other tests are there? I guess it's a case for the EI method.

[tawauboy]

if leave the water sitting for two hours, ph may be change as co2 will diffuse out of the water. the rest of the parameters should not change.
colour chart matching is hard to use. you can use them initially to get a feel of your tank's nutrient requirements. once that is done, you may keep the test kit.

[cdelucia]

Yep, I can get the gist of where the parameters are headed but I really don't have a whole lot of precision with them.

Looks like I'd better do the testing right after take the samples.

Thanks for the answers.