Approaches To Testing Water Samples

[Kaidonni]

I'm curious - how long should I wait after taking a water sample before I conduct any tests? In particular, pH tests - I'm considering the potential for CO2 to be present, and therefore might need to allow it time to outgas. Do I need to wait every time I take a sample, or only if I've recently done a water change (should any CO2 be introduced from the water supply)?

I primarily use the Nutrafin ammonia, nitrite and pH test kits, and the API ammonia and nitrate test kits. Apart from the pH test sample, should I leave any other samples to stand for any length of time prior to conducting tests?

What about washing out test tubes before and after testing? After I'm done testing, I usually just lightly swill them in cold tap water and leave them to dry. Prior to a test, I fill any test tubes I'm using with tank water, shake it about and keep tilting it over and over, then empty - sometimes I do this a second time for good measure - and then I take the proper samples. Recently, I've also swilled the test tubes in cold tap water and dried them with kitchen towel, then done the swilling in tank water before taking the samples. Is there that big a risk of contamination from test reagents not being properly washed out from a previous test?

I also refrain from artificial lighting, and prefer to test in daylight, outside of direct sunlight. I always hold the test tube vertically to avoid tilting the water sample inside. Is it correct to hold the test tube flat against the colour chart, or away from it? I've noticed that when holding directly against the colour chart, there is a degree of backlighting from the white reflective surface of the colour charts. The shadow from the test tube being so close to the chart can also make a test appear darker/impact visibility of the test. I usually do both, holding the test tube flat (but as vertical as possible) against the chart and different distances away from it for comparison. I actually queried this with API, and they advise holding the test tube up against, but not touching the white background on the colour chart. I have asked Hagen, but they haven't yet replied.

 

[TwoTankAmin]

I have always done almost what you describe. here is what I do that may be different or not mentioned.
 
- Rinse the cap the same way as the tube.
- Never dry the inside of the tube or cap. Shaking them a bit to get out some water is fine. Drying outside is OK.
- Rinse before testing with tap, then with tank and then test.
- Take tank water sample from well below the surface to avoid contamination from oils, dust etc. that may be floating there.
- Light source is not hugely important. Having that source of light be from behind or close to above you is. You want it to strike the tube and the sample colors the same way. The light source should not be from the back side of the chart. I find direct bright sunlight makes things harder not easier. I will put the sun behind me and shade the chart and tube with my body in this. "Daylight" works well for me this way. Any room light is fine as it should have a similar effect on the color bars and the sample. It just has to be sufficiently bright so you see the results clearly. Of course no colored bulbs

- I hold it against the paper almost touching the color bars.
 
More expensive and more accurate tests, a kit costing about $80-$90 works better. You fill two test tubes and then you do the test on one, the other is called a blank. You then have a devise into which you insert both test tubes. A color wheel is inside the device. You hold the device so the light is in front of you, not behind as above. The colors on the where are tinted and light goes through them and then through the blank. there are two small windows and you slowly rotate the wheel until the two colors match. There is no guessing as there are many gradations and the colors will match. And impurities in the tested water which might affect the appearance of the color are present in the blank. this makes such test way more accurate and easy to read than hobby kits. A really pricey kit reads the colors digitally.
 
But who wants to spend that much money to test ammonia?
 
The proper amount of time to wait for most test is the one in the directions and pH testing is an exception because of the dissolved gas issues. Unless one is adding co2 gas to a tank, there is no need to wait to test. Established tanks will have a pretty stable pH, even after water changes unless one is intentionally altering tank parameters from the natural ones in their tap.
 
When co2 is being added to a tank for plants, there are regular pH swings between light and dark cycles. The same is true in nature. This is normal. It is rare you will crash a tank from co2 if you are doing it right. If you are worried about co2 levels, consider testing for them rather than for pH.