API phosphate test cloudy - The Planted Tank Forum
 
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post #1 of 5 (permalink) Old 04-24-2015, 08:35 PM Thread Starter
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API phosphate test cloudy

I recently thought I might have excessive phosphate levels thanks to my city's well water quality report so I bought an API phosphate test kit. I first tested my tank water which gave a reading of about 2.5 ppm; high but not as high as I feared.

Next I wanted to test my tap water for a baseline comparison. I washed the test tube and lid as thoroughly as I could using only tap water then tested the tap water. The solution started turning gray when I added drops from the second bottle and got cloudier until gray precipitate started to collect on the bottom. I washed it out and tried again with the same results.

Is this something people have experienced before? Any idea why it would work on my tank water but not the tap water? I was careful ensure that the test tube didn't come in contact with anything else while washing/rinsing it.

Thanks
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post #2 of 5 (permalink) Old 04-25-2015, 01:00 AM
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I can offer a theory:
The second reagent bottle contains tin chloride (SnCl2). The precipitate that is falling out is probably tin sulfide (SnS) which is a gray solid and insoluble in water. It is common for well water to contain hydrogen sulfide (H2S). I believe that in the presence of H2S, the tin chloride is precipitating out of the tap water in the form of tin sulfide.
It would follow that the hydrogen sulfide is not present in the tank water.

What do you treat your water with (and is it worth testing for phosphates after your water has been treated)? Do you know if your source water has traces of hydrogen sulfide? Is your pH high?
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post #3 of 5 (permalink) Old 04-25-2015, 01:16 AM Thread Starter
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Thanks for answering. That makes sense. My pH is about 7.6. I don't remember seeing hydrogen sulfide when I looked at the city water report, but I wasn't really looking for it at the time. I'll check again.

I treat my water with Seachem Prime and dose KNO3, KH2SO4, Flourish comprehensive and Flourish Excel
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post #4 of 5 (permalink) Old 04-25-2015, 02:10 AM
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Quote:
Originally Posted by iceburg View Post
I recently thought I might have excessive phosphate levels thanks to my city's well water quality report so I bought an API phosphate test kit. I first tested my tank water which gave a reading of about 2.5 ppm; high but not as high as I feared.
note: 2.5ppm is NOT high if your tank is planted and you are dosing KNO3... EI low-light doses 1ppm once a week, which in theory accumulates to 2ppm, minus whatever the plants consume.

New to planted tanks, avid gardener/tinkerer.

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post #5 of 5 (permalink) Old 04-25-2015, 08:35 PM Thread Starter
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Thanks Matt. You are right that 2.5 isn't high, it's just a bit above the 1.5-2.0 I was targeting for my mid-tech tank.
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