Can Salt affect API ammonia test reading? Pet of the Month
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Nov 25, 2020
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Short question, can aquarium salt affect the reading of ammonia using the API liquid master test kit?

Background: I have a guppy tank that is cycled, not overstocked or overfed, well maintained and regular water
changes and the fish are doing very well but my ammonia readings for the tank are always around 0.25 (slightly
green). I can't figure out why but then I wondered if it could be the salt. I keep about 1 teaspoon of aquarium
salt per 3 gallons in the guppy tank.

To compare, I tested the water out of my tap and it was more yellow but not as yellow as 0.0 reads on
the test card - but definitely less green. So I added a tiny amount of aquarium salt to my tap water and tested
again and it read 0.25 and slightly green. This makes me wonder if aquarium salt is giving me the small
ammonia reading. Is that possible?
Salt is Sodium Chloride (NaCl) will not give you an ammonia reading because there is no ammonia in the salt.

Salt can make the colour of the solution look cloudy or slightly different in colour but it has to be a lot of salt not just a little bit. If you get a bucket of tap water and test it for ammonia, then add some salt (the same dose rate you use in the tank), then re-test the water and see if that changes the colour. If it does, then the salt is affecting the reading.

If the test kit has a slight green tinge when you test the tank water, but the tap water is yellow, you could have a small amount of ammonia in the tank.

Have you changed anything on the filter in the last month?
Is there anything rotting in the tank (dead plant, fish, uneaten fish food)?

Do a 75% water change and gravel clean the substrate and see if that helps reduce the green.
Thanks for the advice. Yeah, there is always a very slight green color, tap and aquarium, never as yellow as the 0 on the api card. But the green is ever so slightly darker for the aquarium water vs tap. At most, it's 0.25, which I know still isn't good. I'm going to do a gravel (sand) vacuum and test again in 12-24 hours.

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