Water company question

[Jhoussock]

Can anyone explain why I get a reading of 30ppm for nitrates out of the tap, 0ppm after rodi, but my water company (artesian) tells me the nitrates are 2.5ppm in our supply? Is it possible something is wrong with the supply in our home or do they use a different kind of test?

[RogueDiscus]

I don't know the details, but I do think I've read they use a different test. Hopefully someone more knowledgeable will chime in.

[Ryan925]

I read a post here recently that they do do some sort of different test but I don't know the details either

I believe water quality standard is 15ppm or less if I'm not mistaken

[Clawhammer]

Someone get DJW on the line!

[DJW]

It would be nice if we were all using the same yardstick, but we aren't so it can be confusing.

Most water quality reports show measured nitrate in units that are different than the units used in aquarium test kits, while some city water reports use the same units. Check the report where it shows 2.5 ppm and it will indicate which unit is being used.

If it says any of the following:

Nitrate (ppm as nitrogen)
Nitrate (ppm as N)
Nitrate (mg/l as nitrogen)
Nitrate (mg/l as N)

... then multiply by 4.43 to get the same amount that the API or Seachem test would give.

If it says Nitrate ("as NO3") its the same as your test kit.

The EPA maximum is 10 ppm as Nitrogen, which is equivalent to 44 ppm NO3 by an aquarium test kit. In one type of test they are only measuring the weight of the nitrogen, and in the other one (i.e. API) they are measuring the weight of the nitrogen along with the weight of three oxygen atoms. Three oxygen atoms plus a nitrogen atom (NO3) is 4.43 times as heavy as a single nitrogen atom.

So if your water company is using the "as nitrogen" units then 2.5 ppm NO3-N would be 11 ppm by your test kit.

The water quality reports I have seen list the minimum, maximum, and average nitrate over the year. Are they showing 2.5 ppm as the average?

[Jhoussock]

Awesome explanation so the water report I saw is 2.2 as the high and range. That's all that's recorded. Unit is "as nitrogen." I've been using ro water because I thought my nitrates are too high for discus. Is this true? Or should I be going off the water company unit and my nitrates are only in the two's? My API usually shows around 30 on average which tells me stick with ro correct?

[DJW]

Keeping to one type of unit so that we are comparing apples to apples... the city says its 10 ppm NO3 and your test kit says its 30 ppm NO3. It seems like whenever this question comes up the city's nitrate, after converting, is less than what people measure at home. I would like to think the city is using a more precise testing method, but that is a pretty big difference. Have you tried the Seachem test? With the Seachem test you get a result that feels less like guesswork. Another thing you can do is check with your county health dept. to see if they can test it for a small fee.

If it really is 30 ppm I would suggest using ro, or mixing at least half ro with the tap water.