After your reef tank has been up and running for a while, things will begin to happen in your tank; some good and some not so good. Assuming your water parameters start out where they need to be, you’ll see your fish grow, your corals grow and your shrimps and crabs molt. But over time those parameters will change. Your alkalinity will go down. Your calcium will go down and your magnesium will go down. Once these crucial elements are below their expected ranges, the grow of your beasts will slow and eventually if you don’t correct these depletions, the corals will succumb.
So, what to do about all that? Well, to begin with, you need to figure out how much of these components your tank is consuming. Setup a notebook and collect some data. There are many test kits to choose from. Some kits are just not that good. Other kits are costly. Selecting the right kits for testing is something that you will have to either experiment with various manufacturers or select one of the brands I recommend here.
For alkalinity testing, the hands down most popular, easiest to use is Hanna Instruments HI 755 Checker HC Handheld Colorimeter, For Alkalinity (1 cuvette, 1 bottle of liquid reagent and 1 syringe – Included).
For calcium testing, Hanna Instruments HI758 Marine Calcium Checker Test Kit – Saltwater Aquariums.
And for magnesium testing, I would recommend the Red Sea Fish Pharm ARE21415 Saltwater Magnesium Pro Test Kit for Aquarium, 100 Tests.
Generally the ranges to keep your system at are for alkalinity between 8-11 dKh, for calcium between 400 and 460 ppm and for the magnesium between 1200 and 1400 ppm.
Once you’ve tested two to three times minimum over the same time period (every 2nd day or every 3rd day), you should be able to come up with amounts of each of these elements that your tank consumes per day. Now that you have them, you’ll need a method to convert these consumptions into quantities of additives to bring these parameters in range and keep them there by adding chemicals into you tank at a quantity and period consistent with your test results for your tank consumption.
What I do to determine the amounts to add is by going to this URL Bulk Reef Supply and clicking on the calculator icon on the home page. There will be setups for determining how much to add depending on the amount of water in your tank, what the current value is and what is the desired value.
Once you have the quantity to add per day, you must decide if you want to always need to manually add these chemicals or to buy and setup a dosing system to automate this. The doser is the same idea as the IV drip pumps that you see in a hospital. There are many different brands to choose from. There is the Jaebo 4 pump unit Jebao DP-4 DP4 Auto Dosing Pump Automatic Doser for Reef aquarium elements, which is an inexpensive unit that will do. But for the more discerning aquarist, a more exotic unit Aqua-Medic Reef Doser Evo 4 Aquarium Water Pump might float your boat.
After picking your doser, if you decide to go the way of the doser, you’ll need a container for each chemical you top up. A reasonable choice is Marinecolor® Acryli Made Liquid Storage Bucket 3 Rooms 4.5 Liters, Working with Dosing Pump.
Setup for the dosers vary and hopefully the included instructions will provide you with needed information to get the dosing on line.
One last point on dosing your system to mention. As your tank inhabitants grow, the amount consumed will increase. So expect to retest and setup your dosing regimen every couple of months.