API Calcium Test Kit Review: Is it a good kit?

API Calcium Test Kits have long been one of the most affordable brand of test kits available to reefkeepers. But the lower price often causes to people to question how accurate or reliable they are.

Curiosity got the better of me. So, when my Elos test kit ran out, I decided to give the API Calcium Test Kit a try.

Let’s take a look at how the API Calcium Test Kit stacks up against the competition.

Wide availability in large pet store chains such as Petco make it one of the easiest calcium test kits to find.

API Calcium Test Kit

And a price around $10 retail and $7 on Amazon make it, as mentioned, the most affordable kit on the market.

Now, here’s a quick look at how it works.

Using the API Calcium Test Kit:

The API Calcium Test Kits is easy to use.

You simply fill the test vial with aquarium water up to the 5 ml mark. Add 10 drops of the solution from bottle #1. Shake well. Then add test solution from bottle #2 into the vial drop-by-drop until the solution turns blue.

Most other test kits, such as those from Salifert and Elos, involve mixing three or more reagents instead of just two.

There is one slightly annoying catch with using the API test…

You need to shake the vial after adding each drop of solution #2. A plastic cap is included in the kit to cover the vial while shaking. But a little solution does drip down the outside of the vial each time you remove it. And it is cumbersome having to cap and uncap the vial after each drop.

The short cut I use is simple. I toss out the cap and simply hold the open end of the vial against my palm or thumb when I shake it.

Vial mount covered by my palm

You can also add several drops of solution #2 at once if you know roughly where your calcium level is already at. Just switch to adding one drop at a time when you get close to your anticipated endpoint.

The test is complete when the solution changes from pink to blue.

As you get closer to the end of the test, the solution turns purple. That is when you know you only have one or two more drops of test solution #2 before it turns blue.

And the colors along the way – pink, then purple, and finally blue – a vibrant enough to clearly tell apart.

This is about as easy as testing calcium can get.

But what about reliability and precision of the results?

Precision, Accuracy, and Reliability of Results:

Accuracy is where some reefkeepers feel the API Calcium Test Kit falls behind the competition.

It only has an accuracy of 20 mg/l (ppm). Other test kits, such as the Elos kit mentioned earlier, have a precision of 10 ppm.

This wider window of accuracy is the trade off for having to mix just two reagents rather than three or more. It’s also the reason the API kit costs less than most others. Fewer components means less cost to produce the kit.

I have to be honest though, I really don’t find this slightly ‘poorer’ accuracy to be a problem. The more experienced I’ve become at reefkeeping, the more I’ve come to realize that being off by 20 ppm on calcium instead of just 10 will have little to no effect on having a happy, healthy tank.

Think about it. The ideal range for calcium is 400-450 ppm. But that’s for it to be absolutely ‘ideal’. It can fall anywhere between 380 and as high as 550 and still be perfectly fine with happy, healthy corals. And it can even go as high as 600 ppm before there is any real cause for concern or corrective action.

If you have a 50 ppm window to be ‘ideal’ and a 170 ppm calcium range that will keep your reef completely happy and health, a precision of 20 ppm on a calcium test kit is more than enough.

Some of experienced reefkeepers … folks who’ve been keeping tanks for decades … even consider 10ppm to be unnecessary overkill.

And I have to agree. An accuracy of 20 ppm isn’t ‘poor’, it’s perfectly fine. And anything ‘better’ than that is just money wasted on something unnecessary … money that could be used toward more corals, fish, or other equipment.

As far as precision and reliability go…

I’ve tested it several times against both Salifert and Elos calcium tests and it never varied more than 10 ppm from either of them. Which makes sense given both of the other kits have an accuracy of 10 ppm.

So it certainly seems to be reliable.

And multiple tests with the API kit have almost always been spot on with the same reading … only varying by 20 ppm once in a very great while. That’s more than enough precision to ensure your calcium stays in a range that will keep your corals happy.