Dosing 101: Keeping Alkalinity, Calcium & Magnesium Steady

"Dosing" sounds like the deep end of the hobby, but the idea is simple: growing coral eats certain elements out of your water, and you put them back. Get this one routine right and your reef rewards you with color and growth. Here's the plain-English version.

Why you dose at all

Coral builds its skeleton from calcium and alkalinity (carbonate), with magnesium keeping the chemistry balanced so the other two stay in solution. As your corals grow, they pull these from the water faster than water changes replace them — and levels drop. Dosing tops them back up. The big three:

When to start

Not on day one. A young or lightly-stocked tank's demand is so low that regular water changes alone replace what little gets used. You start dosing when your testing shows a consistent daily drop — usually once you've got a few growing corals. Until then, dosing just risks overshooting.

Choose your method

2-part is the beginner standard: one bottle of alkalinity, one of calcium (magnesium dosed occasionally). Simple, cheap, infinitely adjustable. All-in-one balanced supplements dose everything in correct ratio from a single product — even easier, ideal for lower-demand tanks. A calcium reactor is an advanced route for big, hungry SPS systems — skip it until you're well past the basics.

Supplements

Red Sea Reef Foundation A/B/C · $22
A clean, popular 3-part (alk / calcium / magnesium) — a great first system you can dial precisely.

BRS 2-Part Calcium & Alkalinity · $30
Excellent-value 2-part that lets you dose exactly what your tank consumes.

Tropic Marin All-For-Reef · $40
A balanced all-in-one that supplies alk, calcium, magnesium and trace in one bottle — beautifully simple for lower-demand reefs.

Manual or automatic?

Early on you can dose by hand once a day — totally fine. But the magic of dosing is consistency, and nothing's more consistent than a pump that doses small amounts on a schedule while you sleep. A doser turns alkalinity from a daily swing into a flat line, which is exactly what coral wants.

Dosing pumps

Jebao Doser 3.1 Single · $60
Automate your alkalinity first — the highest-impact, lowest-cost place to start.

Kamoer FX-STP · $165
Quiet and accurate with app control for one parameter.

Kamoer X4 Pro · $269
Four heads to dose your full 2-part-plus-trace routine on autopilot.

Neptune DOS · $300
Precise two-head dosing that integrates with an Apex controller.

And the test kit that guides it all

Red Sea Reef Foundation Test Kit · $45
Dosing without testing is guessing. This tracks all three so you dose to your tank's real demand.

See it all in Dosing & Testing — and pair it with automation when you're ready to go hands-off.