Ammonia test and very hard water


Here is a question I have wondered about for many years.

The ammonia tests on all our freshwater tanks come in at zero on the saltwater card and a bit below.25 ppm on the freshwater card. Even on extremely stable long established aquariums. This is across many different API test kits over the years. Bottled water shows a true yellow zero with the same test. But on some other test kits I have to use the saltwater cards to match the colors produced.

Our water is extreme with a very high TDS, and pH buffers at 8.2 - 8.6 and tanks with 2/3 RO water buffer at about 8.0.

Is it possible that something in our water makes it behave like saltwater for purposes of the API ammonia test (and others)? Is there some type of amine that triggers the sodium salicylate in the reagent? Below are our tap water tests for any chemists out there.
Thanks for any help on this mystery as it always makes us wonder when a cycle on a new tank is truly complete.

Alkalinity (mg/L as CaCO3)

Calcium (ppm)

Hardness, Calcium (mg/L)

Magnesium (ppm)

Potassium (ppm)

Nitrate as N (ppm)

Sulfate (ppm)

Sodium (ppm)

Gross Alpha, inc (pCi/L)

Copper (ppm)

Lead (ppb)

Total Trihalomethanes (ppb)


I’m not an expert but my water parameters are

PH : 8.1
GH : 304 ppm
KH : 125 ppm

And I am able to reach the same color for 0 ammonia as the tap water. But sometimes there is a very slight green tinge to it and I have to compare with tap water to convince myself it’s fine.

When I had my planted tank with a PH of 7.0, GH 50 ppm and KH 100 ppm, it was a lot easier seeing the 0 ppm ammonia because the test came out a « true » medium yellow.

So you might be right, it’s harder to read. But I’ve only had my tank running for a 5 months and during that time I had 2 ammonia spikes (due to mistakes on my part) so maybe I wouldn’t say the same in a year from now.
  • Thread Starter


Same here, when I really dilute the tap water for certain fish I can reach a true yellow on the test kit. Your water parameters are just about what I run for our "soft water" fish when I cut with 60% rain or RO water.


I'm going to dig into this one. I don't have an answer now but when I get a free minute I'll give in. Are the numbers you posted all from your own test kits or did you send in a lab sample somewhere?

I ask because the calcium and "hardness calcium" are written contradictory, perhaps the later should be "hardness GH", a sum of calcium and magnesium typically. Also, testing for magnesium, and potassium is pretty tricky without a lab.

If you're mixing results of diy and lab, coming up with a sum and missing link will be very difficult. Could you "*" tests from an outside source, if using multiple outside sources find a way to express that.

I do bet you are correct in there being more to the test colors for saltwater than just specific gravity/salinity and will do some digging later. Awesome thread.
  • Thread Starter


These are all taken directly from the lab results for our water district. It is ground water so these values stay constant.

I have wondered about some of the wording regarding calcium. Both these were on the same lab report. Maybe utilities state certain values differently than we are used to seeing. My own calcium tests ran around 250-270 ppm.

My TDS readings out of the tap are 620 ppm.

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