Keeping a thriving reef tank means giving your corals the right building blocks every single day. That’s where reef dosing comes in. Instead of relying only on water changes, dosing lets you replace key elements that corals and coralline algae consume as they grow. Done correctly, it leads to better color, faster growth, and a more stable, predictable system.

What Is Reef Dosing and Why Does It Matter?

Reef dosing is the controlled addition of supplements to maintain stable water chemistry. In most mixed and SPS-heavy systems, three things get used up quickly:

• Alkalinity (dKH) – supports coral skeleton growth and pH stability.
• Calcium (ppm) – combines with carbonate to build skeletons.
• Magnesium (ppm) – keeps calcium and alkalinity in balance and helps prevent precipitation.

Other elements like potassium, iodine, and trace metals can matter too, but you’ll get 80–90% of the benefits by nailing these three first. If you’re brand new to water chemistry, read our Reef Water Parameters Guide before you start dosing.

Finding Your Tank’s Daily Consumption

Before setting up any dosing schedule, you need to know what your tank actually uses each day. Guessing leads to instability, which is the opposite of what you want.

Step-by-step testing routine

• Step 1: Test alkalinity, calcium, and magnesium at the same time each day for 4–7 days.
• Step 2: Record the results in a notebook or app.
• Step 3: Do not dose during this period (normal water changes are fine).
• Step 4: Calculate the average daily drop for each parameter.

Example: If alkalinity falls from 8.5 dKH to 7.5 dKH over 5 days, your tank is using about 0.2 dKH per day.

Once you know your daily consumption, use your supplement manufacturer’s dosing chart (or calculator) to figure out how many milliliters you need to add to maintain your target levels.

Manual Dosing vs. Dosing Pumps

There are two main approaches to getting supplements into your tank: manual dosing and automated dosing pumps.

Manual dosing

• Use a measuring cup or syringe to add supplements once or twice per day.
• Best for smaller tanks or lightly stocked systems.
• Keep it consistent: same time of day, same amount, and re-test weekly.

If you’re still building your system, our Beginner Reef Tank Setup Checklist can help you decide when it’s time to move from manual to automated dosing.

Dosing pumps

• Deliver small amounts of supplement throughout the day for greater stability.
• Ideal for tanks with lots of stony corals or clams.
• Let you spread your daily dose into multiple tiny doses (for example, 12–24 times per day).

Place dosing lines in a high-flow area of the sump, away from skimmer intakes and not directly next to each other, to avoid localized precipitation when different solutions meet.

Practical Dosing Tips for Long-Term Success

• Change slowly: Aim to adjust alkalinity by no more than 0.5 dKH per day.
• Test regularly: Weekly for stable tanks; every 2–3 days when making changes.
• Label everything: Clearly mark containers and pump heads to avoid mix-ups.
• Watch your corals: Pale tissue, burnt tips, or rapid algae growth often signal dosing issues.
• Coordinate with water changes: Large water changes can reset levels; re-test afterward and tweak your schedule.

For a deeper dive into keeping your system steady, check out our Reef Tank Stability Tips page.

Reef dosing doesn’t have to be intimidating. Start by understanding your tank’s consumption, then match your dosing to those needs and make small, measured adjustments. With consistent testing and a simple routine, you’ll keep your parameters rock solid—and your corals will reward you with steady growth and vibrant color.