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API Saltwater Calcium Test Kit


Item #: AP3137

In Stock

This kit allows for easy and accurate measuring of calcium levels to help in maintaining a healthy aquarium.

Why test for Calcium?
Monitoring calcium levels is essential for keeping a successful reef aquarium. Reef organisms use calcium to build a calcium carbonate skeleton. Over time, as the calcium in the water is utilized, the calcium level will gradually drop. Calcium must be present for corals to grow. Even reef invertebrates such as crustaceans, mollusks and encrusting algae, require calcium to grow and remain healthy.

Calcium levels drop as it is used by invertebrates or as it reacts with excess phosphate. Making a partial water change may help to maintain proper calcium levels, depending on the brand of salt mix. Special calcuim additives are also available. Elevated phosphate precipitates calcium, rendering it unavailable to reef organisms. Phosphate enters the aquarium from tap water and as a byproduct of fish and invertebrate metabolism. Use Aquarium Pharmaceuticals Phosphate Test Kit to test for phosphate. If necessary, use Aquarium Pharmaceuticals Phos-Zorb™ to remove excess phosphate. Phos-Zorb is a special phosphate-removing filtration media that comes in a flow-through pouch. It conveniently fits into any filter.

Carbonate hardness (KH), often referred to as alkalinity, is important for reef organisms. As carbonate levels drop the pH becomes unstable. The carbonate hardness level (KH) should be 7-10 dKH [125 – 179 mg/L (ppm)] to encourage growth in a reef aquarium and maintain pH. Use the Aquarium Pharmaceuticals KH Test Kit to measure the carbonate hardness. Add Proper pH 8.2 to increase carbonate hardness and stabilize the pH to 8.2.

Manufacturer information

Aquarium Pharmaceuticals Aquarium Supplies
Aquarium Pharmaceuticals (API) has been helping people take good care of ornamental fish for over 40 years. Their research and development scientists have advanced the care of fish with all-natural medications, stable bacteria for biological filtration, one-bottle test kits, consumer-friendly dosing caps and much more. They’ve received over 25 global patents for their breakthrough innovations in the aquatics industry. And they continue to look for ways to improve the fishkeeping experience for hobbyists. Research. Experience. Dedication to scientific, quality treatment for healthy fish. It’s what makes API the first choice of aquarium owners. API manufactures and sells hundreds of products across many different product categories, including aquarium and pond treatments, aquarium equipment, aquariums and fish nutrition.

4 Stars


Reviewed on
December 24, 2019

Yes, I would recommend this.

Calcium test kit

Pros: Price and ease of use.

Cons: Gives approximate measurements

I have been using this test kit for over 6 years now. It may not be the best kit for exact measurements, but it is excellent for trends and is very easy to use. I would not be without it. It is quick, easy and the price is right. It is my primary calcium kit. But I do use a second test kit as a back up for more exact measurements when I notice variances with my API kit.

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Reviewed on
July 20, 2019

Yes, I would recommend this.

Good calcium test

Pros: Easy to use and consistent

Cons: Titration is never fun

Good calcium test. It's the standard titration test. I recommend always doing one drop beyond what you think is the final color so that you really know where the endpoint is, just don't count that last drop towards your system values.

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Reviewed on
July 10, 2019

No, I would not recommend this.

Not very consistent

I can say that the test kit doesn't really provide consistent results which to be fair isn't that great any most other Calcium test kits.

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Reviewed on
May 17, 2019

Yes, I would recommend this.

easy to use

Pros: easy to use

Cons: not very accurate

the stuff is basic .just add drops until changes color

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Reviewed on
April 06, 2019

Yes, I would recommend this.


Pros: Works

Cons: Gotta use it to make it work.

Works for all you need for basic marine water testing.

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Reviewed on
March 25, 2019

Yes, I would recommend this.

does the job

Pros: complete kit with nice glass tube

Cons: dropper bottle isn't as accurate/consistent as a syringe

Clear instructions. Easy to read. It does the job for a decent price.

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Reviewed on
February 11, 2018

Yes, I would recommend this.

API Calcium test kit

I like this kit its fast, easy and accurate.

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Reviewed on
December 29, 2017

Yes, I would recommend this.


Pros: Inexpensive

Cons: None

Affordable easy to use

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Reviewed on
September 12, 2017

Yes, I would recommend this.

Good test kit

Pros: Easy to read color chart

Cons: Bottle 1and2 not proportion correctly 2always runs out sonner they need to fix that.

Very easy to use and fast

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Reviewed on
May 06, 2017

Yes, I would recommend this.

Not that bad?

Pros: Inexpensive, multiple tests performed, easy to use and determine color change.

Cons: None for me

So it is consistent. Probably fairly accurate, but have not tested against other optons. Works well enough for my need.

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