API test kit changes color after 15 minutes !! Accuracy related thread ...

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nsamuel

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Apr 3, 2008
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Today i noticed something about the API tests. I was running Ammonia, ph and nitrite tests. All of them develop in 5 mins, but given more time, they develop into slightly stronger colors with minor variation in the result. For example, my ph would read 7.2 soon after proper test, but given 15 minutes it developed into 7.3, a noticable color change to my discerning eyes. Also the nitrite showed minor change, but noticable if given careful consideration to lighting and correct reading of color chart. The ammonia colors change for me over a period of hours, but this could be because the bacteria and and other microorganisms grow faster in the test vial rather than my tank thats cycling. They might be eating up the ammonia present in the test vial causing the color change.

So, i am thinking maybe API gives the 5 minute time frame so that the customers dont have to wait too long to see the results. Perhaps waiting 10 minutes would give a more accurate result. Has anyone else noticed this ? Any ideas ? BTW, my test kits are brand new bought a month ago, and i make sure that i read the colors during daylight with accurate method of reading without shadows cast on the colors.
 
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Come to think of it, when I first started using them the PH changed color to harder. After that mine stopped changing color when i left them for hours. Then again, my tanks def. have 0 ammonia, 0 nitrite, and the number of nitrate holds steady respectively (10 and 5). I usually now read after 5 minutes has past.

Would you consider changing one of the tags to "of interest"?
 
I guess you can test only for ph change since other readings are low for you. Can you try a ph test in daylight and see how it changes in 15 minutes ?

For the others who might be reading this thread.....
I have found that the indoor lights do not produce accurate results like well sunlit area. Also, the color changes are harder to notice in indoor lighting. Especially useful to keep this in mind for sensitive tests. Also, note that proper holding of the tube and having light fall on the tube at right angle, and viewing the tube in the right direction, all play a role in accurately reading the colors.

Actually, i have left my all tubes for 24 hrs to check. They produce one result at the end of time stated in the manual. Then the colors change after 10 or 15 minutes. Then, ph showed no change for many hours, and maybe showing slight change when i checked the next day. I think the most important factor is the first 15 minutes. I will pay careful attention to how the colors change over 24 hrs in the next few days, by storing them again and paying close attention to them this time after a day. I know Ammonia color changes quite a bit after 12 hrs, but that could be because of other factors in the water. But i doubt if bacteria could play a role in color change in a short time like 15 minutes.
 
I left mine in the tubes for over a month. There may have been a slight change in the color, but I didn't notice. Ammo and Nitrite definitely still read 0. I did, however, notice the solution collecting at the bottom of some tubes, mainly the Nitrate...wasn't easy to get out. :)

I'm sure the whole "wait 5 minutes" isn't for the benefit of the customer as much as it is for an accurate reading.
 
API probably gave the time frame for a reason - that's the most accurate time frame.

I know that with many in-clinic (at least, veterinary) laboratory tests that are based on a color change, or are read on a range of color like the water test kits, you have to read the color change at the time indicated. You need to give it at least that much time so that the chemical reactions will have taken place (especially when you might be testing for the presence of something that is in a relatively low concentration, for example). After that time, the chemicals that produce the color change are still present, and may react with things other than what the test is supposed to indicate (I think these are generally less favorable reactions; i.e., the chemicals will preferentially react with what they're supposed to, and then if there's anything around that is kind of like its preferred substrate, it'll take that as a second choice after a while) and cause false readings if given sufficient time. Eventually, the reagents run out, so the color would not change beyond a certain amount. These kind of things are developed by the company in question to be convenient (i.e., the reaction will take place within a certain, relatively short, time frame) and easy to read (match up colors, or whatever), and have a relatively low margin of error (i.e., not give too much or too little time for the reactions in question).

As far as ambient lighting is concerned, sunlight is always best when attempting to determine the color of anything. Our eyes are evolved to accept sunlight as "white" light (even though physics tells us it's actually a yellow light). Therefore, that's the type of light we're best suited to discern small differences in. The average household light is a yellower spectrum, and our perception of color is affected by the type of light that's bouncing off of the surface, so it stands to reason that you would perceive the color as being a little different. I would imagine that "daylight" spectrum light bulbs would be adequate for color perception as well.
 
schizo - changed the tag as you requested. May i ask why you wanted it ?

equus - On second thoughts, i agree with you, because i remember my chemistry lab experiments from long time ago. The time has to be adhered to. Also, on second thoughts, i think the color changes might be because my tank is cycling and is full of bacteria in water with high ammonia too. The ph is fluctuating wildly also, as i am doing a fishless cycle with ammonium hydroxide. So, the bacteria might be consuming the ammonia in water resulting in color changes after sometime. But this would be a good experiment to try for someone like schizo who has ammonia and nitrite at zero and stable ph.

I am mostly interested in the color at exact indicated time, and 10 minutes thereafter. So two readings taken 10 minutes apart should be good enough to tell if there is really any difference. Sometimes i feel that the color actually stabilizes only at 10 mins or so, and never changes after that.
 
because I think that threads like this should be tagged on the site with easy access, and the "of interest" tag is already in use and this is certainly of interest. I mean, it may be better to put it also under "liquid test kits" or something, but I haven't really seen much come up under that category.
 
Follow the recommended time frame. Waiting longer does not give you a more accurate result.
 
SchizotypalVamp said:
because I think that threads like this should be tagged on the site with easy access, and the "of interest" tag is already in use and this is certainly of interest. I mean, it may be better to put it also under "liquid test kits" or something, but I haven't really seen much come up under that category.
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Good idea schizo. Because its so hard to search for anything useful and narrow down the search with the current search engine on this site. I suggest using google to search this site with the modifier site::aquariacentral.com which will produce more accurate results and helps narrow to what you really want.

I just want to clarify..... i had enough chemistry in college to understand that waiting too long after a test will produce inaccurate results. For example, my nitrite vial which showed 0.15 (after 5 min thats manual time) turned to 0.25 when left to sit for 12 hrs. But, i thought this is an interesting thread to start because the color also changed to 0.20 area within 10 mins of test, which i found to be worth a discussion. Remember that all these tests have a little bit of inaccuracy in them simply because these reagents are not laboratory grade regents which cost more (hach, lamotte etc.). I have not done a search on net to find out how good API nitrite is compared to salifert etc. But i do know that API nitrate and alkalinity tests are reported as inaccurate. But are good enough for freshwater purposes. After a few weeks or so when i have a chance i will run a side by side test using Instant Ocean, which is laboratory grade regents. Will resurrect this thread at that time.
 
rbishop said:
Follow the recommended time frame. Waiting longer does not give you a more accurate result.
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I agree...the colors intensify and give inaccurate results. I left the tubes out too long and found that I had off the chart levels of both nitrite and nitrate after one day of adding ammonia to the cycle:grinyes:
 
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