Multiple salifert test kits giving different results

[Marc2952]

I recently got a salifert calcium kit since my old one was running low. To my surprise though they both told different results by a large margin, my old one reads 425 while the new one reads 490. How can i know which one is correct? Because for weeks i tested mines at 445 and dipped to 420 today on the old one. I just wanna make sure i keep it stable since im dosing 2 part.

 

[TexanCanuck]

In my experience, these test kits are not overly accurate or highly repeatable. I believe they are meant to provide you more of a relative indication, rather than be relied on for an exact number.

Think about it this way ... the difference between 490 and 425 is only 15% ... I wouldn't expect these kind of test kits to offer an accuracy much greater than 10% ... so these two measurements are definitely different, but based on the time of day and the difference in kits the difference may not be as big as you think.

Also be prepared that there will be inevitable swings in calcium levels on a daily basis. The key is to maintain them greater than 360ppm, which is the lower boundary at which it becomes difficult for corals (and some macroalgaes) to grow.

In c are it helps to compare, I am using a Neptune Systems Trident to measure calcium levels in my tank twice a day and use it to automatically adjust my dosing amount, and here is the resulting fluctuation in CA levels I get:

For a more in-depth discussion on ideal calcium levels, see Randy Holmes-Farley's article on ideal water parameters ... scroll down a little past the tables to see what he has to say about calcium in particular.

Optimal Parameters for a Coral Reef Aquarium: By Randy Holmes-Farley

[note: edited on 5/29/2022 to update the nitrate and phosphate sections with higher recommended levels.] One of the main roles of an aquarist with a coral reef aquarium is to ensure that the conditions are right for their tank inhabitants. There...

www.reef2reef.com

 

[Randy Holmes-Farley]

Both values are fine and I'd just assume it is in the 400's.

 

[Marc2952]

Both values are fine and I'd just assume it is in the 400's.

So for now keep dosing equally and test in a couple days to see if it keeps dropping to adjust?

 

[rusgum]

I recently got a salifert calcium kit since my old one was running low. To my surprise though they both told different results by a large margin, my old one reads 425 while the new one reads 490. How can i know which one is correct? Because for weeks i tested mines at 445 and dipped to 420 today on the old one. I just wanna make sure i keep it stable since im dosing 2 part.

When I open a new test, I always check it with a reference liquid and make a correction when measuring.