Salt Water Aquarium Testing & Dosing

Once you have your reef tank up and running and have added your first corals it is time to start monitoring water parameters.  Water testing can be divided into two categories, testing of nitrates and phosphates to control algae and the monitoring of major and minor elements to promote coral growth and health.  Since phosphate and nitrate levels can usually be controlled through effective filtration and water changes this guide will focus on the three most important elements required for a thriving reef tank; alkalinity, calcium and magnesium.  These are often referred to as major elements.  There are countless other minor and trace elements but they can generally be maintained through water changes and do not usually require active monitoring and dosing.

The major elements, especially alkalinity and calcium, are used by corals to build their stony skeletons and so they will deplete over time.  Their levels can be increased and maintained usually in smaller aquariums simply through water changes.  Early on, the levels of these elements can likely be maintained through regular water changes, but as corals grow and more are added they will consume more than can be replenished through water changes alone and dosing may become necessary.


So how do you know when it’s time to start dosing your reef tank?  By testing your water on a regular basis.  Regular testing will give you a good idea whether it is time to start dosing and how much to dose.  There are two basic methods to test water parameters, either with a digital tester, such as those made by Hanna, or a reagent test such as the popular Salifert testing kits.  Because the digital testers require both the purchase of the tester as well as the reagents to perform the tests, the Salifert kits tend to be more economical.  Now that you have purchased the test kits of your choice it’s time to test the water.  A good way to start is to check your levels after your weekly water change and then again right before your next water change as this will give you an idea of the rate your corals are consuming the elements.  Alkalinity should be kept in the range of 8-12 dKH, Calcium at roughly 380-450 ppm and Magnesium around 1400 ppm.  While the values should be in recommended ranges, the key is not to aim for a specific number but rather to ensure that the levels stay consistent in the aquarium.

Once you have identified that your corals are consuming the elements faster than they can be replenished by water changes it is time to start dosing.  There are many different ways to dose a reef tank, each with their own pros and cons.  For a Reef Casa sized aquarium the best options are either an all in one product such as Tropic Marin’s All for Reef which combines alkalinity, calcium, magnesium as well as other minor and trace elements in one additive or Red Sea’s line of separate alkalinity, calcium and magnesium additives.  Both methods will include instructions for how much to add to raise the desired element by a set amount.  At this point you can use the weekly consumption rate that you calculated to determine how much to add on a weekly or daily basis.

So what is the best way to dose additives to your Reef Casa aquarium?  There are two methods, either manually with a syringe or small measuring cup (usually included with the additives) or through the use of a dosing pump.  It is important to remember that if you are dosing alkalinity, calcium and magnesium separately you will need a dosing pump with three heads, whereas if you choose to use Tropic Marin’s All for Reef you will only need a pump with a single head, which is significantly less expensive.  Either method will work perfectly fine, it just comes down to a question of cost vs. convenience.  Many reefers eventually find that a dosing pump is a worthwhile investment and single head models can be found for about $100.

While reef tank dosing may seem overwhelming at first, and make you wish you had paid more attention in chemistry class, effective and regular testing combined with a few simple calculations can make a world of difference and set you up for reefing success.  If you have any questions about additives or dosing please reach out to us, we are here to help.  Happy reefing!