Question about water measurements with test kits.

ShakeyGizzard · May 28, 2026

I have been using Salifert test kits for ages, i only use API when cycling a tank, But adding 5 ml to an API test tube does not look correct when using the 5 ml syringe in Salifert test kits.

With this being said, I can weigh out 5 ml of 35 ppt saltwater to 5.11 to 5.13 grams at room temp and use that to check the API and salifert syringe to see how close they are. They are subjective based on your view of each receptacle. But the real Question is, what did they use to measure when determining the amount for the reagents in the test kits. Did they use the actual syringe and test tube or something else. anybody know

Fish Fan · May 28, 2026

I'd be inclined to trust the Salifert syringe more than the line on the API tube. There shouldn't really be any subjectivity with reading the syringe, Randy has a post on the correct way to use a syringe for test kits:
https://www.reef2reef.com/threads/reef-chemistry-question-of-the-day-161-using-a-syringe.226267/
I hope this helps!

Randy Holmes-Farley · May 28, 2026

What sort of test was the api tube for?

In some tests, water volume is not very important. These include tests that involve color matching to a card.

Tests where volume is important as those where you add a titrant to get to a specific color.

Fish Fan · May 28, 2026

Randy Holmes-Farley said:
What sort of test was the api tube for?

In my experience, all API tests are based on a 5 mL volume, and all tests kits that I've had come with the same tubes where that line is supposed to indicate 5 mL. I don't believe I've seen anything else fromm API, freshwater kits included; the tubes seem entirely interchangeable from kit to kit.

Randy Holmes-Farley · May 28, 2026

Fish Fan said:
In my experience, all API tests are based on a 5 mL volume, and all tests kits that I've had come with the same tubes where that line is supposed to indicate 5 mL. I don't believe I've seen anything else fromm API, freshwater kits included; the tubes seem entirely interchangeable from kit to kit.

thx. Certainly, the volume measurement for ammonia, nitrate, nitrite and phosphate kits are not critical.

ShakeyGizzard · May 29, 2026

Randy Holmes-Farley said:
What sort of test was the api tube for?

In some tests, water volume is not very important. These include tests that involve color matching to a card.

Tests where volume is important as those where you add a titrant to get to a specific color.

Just testing ammonia level for cycling a new tank, i use salifert for tests