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Issues with testing kits


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I'm having some issues with the accuracy of my water testing kits and was hoping the NERMs here can help me out.

Initially I thought I had "old tank syndrome," since this tank has been running for approximately 3 years. It is very heavily planted and I have stopped adding liquid fertilizer the past 3 weeks to try and get this nitrate issue under control. My nitrites and ammonia are zero, but nitrates are showing between 80ppm and 160ppm according to the API master test kit (widely regarded in the hobby as the most reliable/accurate.) I have been playing with the Tetra test strips as well, and it shows the nitrate at 40ppm. Its still higher than I'd like, but shows that my efforts at correcting the issue might be working.

I did a 30% water change last week but nitrates stayed steady. I did a 40% water change today and the API test kit still shows no change in nitrate levels. I would expect to see SOME improvement, as I have also been making a concerted effort to feed less and also cleaner foods (holding off on Repashy, for example.)

I've tested my other tanks too, including ones that have not been running for too long (around 3-4 months, set up with a mature sponge filter and about 50% water from a mature tank) and I'm also getting very high nitrate readings, 40 to 80ppm. That doesn't seem realistic. Possible yes, but unlikely.

I have checked the expiration dates and everything is well within working range. My tank is probably overstocked, so I am not completely innocent in all this, but I am very confused that I'm getting such different results.

What do you guys use that you feel is the most accurate? I hate that all these tests are color based, I'd much rather get a reading from something like a pH meter. (*Insert science background rant here.*) Obviously I'll need to adjust stocking levels, but I need a way to monitor if I'm making progress!

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Yes, I have been following the written directions to a tee. I shake both bottles for 1 minute before testing, and I also shake for 1 minute after adding both reagents (per directions.)

I have not tested my tap in the past 3 weeks so I will test that and post results here.

Edited by Kat_Rigel
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25 minutes ago, Bill said:

Also, I have had API test solutions that seemed slightly off. I compared to the tap water and determined some readings were registering high, for example, ammonia that was really zero showed as 0.25. This also happened with an API phosphate test.

🤔 Hm, interesting. Well, I tested my tap and it is showing between 20 and 40ppm nitrate, which explains a lot. I am going to pick up a new API liquid nitrate test to compare; either the test is wonky (as you refer to above,) or I should switch my water source for a little while until my tap water becomes more normal.

Sometimes it's the simple stuff; every time O think I'm getting the hang of fishkeeping, I ignore some small thing because it seems too simple. 😅 Good thing my fellow NERMs can help me out!

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  • 2 weeks later...

I use two other nitrate test kits in addition to the API test tube kit. I won’t mention any brand names for my comparison, other than the subject brand. 
I did all three at the same time. Followed the directions to the letter. 
API read a very solid orange indicating 40ppm. 
Brand X read a faint pink somewhere in between 10 &25 ppm. 
Brand Z read bright yellow indicating no nitrates...or less than 10 ppm. 

Who to believe?
I continue using the API test despite the fact that I think it’s reading high. It’s the test that I’ve used since day one so I can gage the ups and downs. I think of it like a speedometer that reads 20 mph too high. So as long as you know how far off you are you can drive 45 mph though the school zone and give a friendly wave to the cop with the radar. 

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On 11/1/2020 at 1:55 PM, Kat_Rigel said:

My nitrites and ammonia are zero, but nitrates are showing between 80ppm and 160ppm according to the API master test kit (widely regarded in the hobby as the most reliable/accurate.)

The API liquid test kit for Nitrate is notoriously unreliable, you really have to shake it and bang it to do it just right, I personally really prefer the tetra 6 in 1 strips and found them to be very accurate. The API liquid test kit is the gold standard, but the ammonia test is very commonly misunderstood and the nitrate test is very easy to mess up due to it needing to be vigorously shaken for 60 seconds before adding the drops to the vial. Can't wait for Cory's test strips! 

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