Dosing for Reef Aquariums: How-To Guide | Myreeflog

Why Dosing Matters for Reef Health

Corals build skeletons from calcium carbonate. Every day they consume alkalinity (carbonate and bicarbonate) and calcium from the water, along with a small amount of magnesium that keeps those ions in solution. If you do not replace what is used, levels drift, growth slows, and sensitive corals show stress. Stable, appropriate levels are the foundation of a thriving reef.

For most reef aquariums, target the following ranges: alkalinity 7.0-9.0 dKH, calcium 400-450 ppm, magnesium 1280-1400 ppm, salinity 35 ppt (SG 1.025-1.026 at 25°C), and pH 7.8-8.3. This dosing task guide focuses on two reliable approaches - two-part dosing and kalkwasser - that keep these parameters steady. Platforms like myreeflog make it easier to see consumption trends and match your dosing to the actual needs of your system.

Consistent tracking removes guesswork. With My Reef Log, you can chart alkalinity and calcium over time, calculate daily consumption, and set reminders so dosing becomes a simple, repeatable routine instead of a stressful scramble.

When and How Often to Dose

Newer tanks with few stony corals may get by on regular water changes for a while. You know it is time to start dosing when your alkalinity drops more than 0.2 dKH in 24 hours or calcium drops more than 10 ppm over a few days. SPS-dominant reefs and systems with heavy coralline growth often need daily dosing from early on.

• Two-part dosing frequency: for best stability, spread the total daily amount into multiple small doses. Hourly micro-doses or 4-12 dose blocks per day work well. Avoid large single additions.
• Kalkwasser frequency: dose slowly and continuously as part of your top off, ideally concentrated toward the evening and overnight to help stabilize pH when lights are off.
• Testing cadence: test alkalinity daily at the same time for the first 7-10 days while dialing in. Once stable, test alkalinity 2-3 times per week, calcium weekly, and magnesium every 1-2 weeks.

What You'll Need

For Two-Part Dosing

• Alkalinity solution: sodium carbonate (soda ash) or sodium bicarbonate. Soda ash raises pH more, bicarbonate has a smaller pH effect. Popular kits: ESV B-Ionic, BRS Pharma 2-Part, Red Sea Reef Foundation B (alkalinity).
• Calcium solution: calcium chloride solution. Examples: ESV B-Ionic, BRS Pharma 2-Part, Red Sea Reef Foundation A (calcium).
• Optional magnesium solution: magnesium chloride and magnesium sulfate blend for periodic corrections.
• Accurate test kits: Hanna Alkalinity Checker or Salifert/Red Sea, Salifert or Red Sea for calcium, Salifert or Red Sea for magnesium.
• Dosing pumps and containers: peristaltic pumps like Neptune DOS, Ecotech Versa, Kamoer X1 Pro, or Jebao DP-series, plus chemical-resistant containers and dosing tubing.
• High-flow area for dosing: return pump chamber or a high-turbulence zone.
• Safety gear: nitrile gloves and safety glasses.

For Kalkwasser (Calcium Hydroxide)

• Kalk powder: food grade or aquarium grade calcium hydroxide. Examples: Two Little Fishies Kalkwasser, Brightwell Kalk+2, BRS Kalkwasser.
• RO/DI water: the cleaner the better to minimize impurities.
• Container with lid and a way to keep the pick-up line off the bottom. A 5 gallon food-safe container works well.
• Delivery method: a reliable ATO like Tunze Osmolator 3155 or a dedicated peristaltic pump for controlled drip.
• pH meter or probe recommended to watch for spikes.

Step-by-Step Process

Two-Part Dosing: Establish and Maintain Stability

1. Establish a baseline. Test alkalinity, calcium, magnesium, salinity, and pH at the same time of day for 2-3 days. Adjust salinity to 35 ppt before you make any other changes. Correct magnesium into the 1280-1400 ppm range first because low magnesium encourages precipitation.
2. Measure daily consumption. Stop dosing for 48-72 hours, feed and maintain as usual, then test alkalinity at the same time each day. Daily alkalinity consumption (dKH/day) = ALK_day1 - ALK_day3 divided by the number of days. Expect roughly 0.1-0.3 dKH/day in a light mixed reef, 0.5-1.0 dKH/day in a growing mixed reef, and 1.0-2.0 dKH/day or more in an SPS-dominant reef.
3. Calculate a starting dose. Use your product's dosing chart or online calculator to convert daily dKH consumption into mL per day for your system volume. As a rough chemistry guide, corals consume calcium in a ratio of about 18-20 ppm Ca for every 1 dKH of alkalinity used. That ratio helps you match calcium dosing to alkalinity demand.
4. Start low, split doses. Begin with 50-75 percent of the calculated dose and split it across the day. For example, if you need 60 mL per day, start with 30-45 mL split into 6-12 equal doses. Smaller, more frequent doses create flatter parameter curves.
5. Dose alkalinity and calcium separately. Add alkalinity solution into high flow and allow at least 10-15 minutes before dosing calcium to avoid localized precipitation. Keep the ends of the two dosing lines several inches apart.
6. Retest and adjust. Test alkalinity 24 hours after starting. If it is still dropping, increase the total daily alkalinity dose by 10-20 percent. If it is rising, reduce by 10-20 percent. Once alkalinity is stable day to day, align calcium dosing to hold calcium steady within 10 ppm week to week.
7. Fine tune pH effects. If your pH typically runs below 7.9, choose sodium carbonate for alkalinity to nudge pH upward. If your pH is already high, sodium bicarbonate may be better.
8. Keep magnesium in range. Test magnesium weekly at first. Correct back to 1280-1400 ppm when it drifts more than 50-80 ppm. Do not raise magnesium by more than 100 ppm per day.
9. Limit daily changes. Avoid increasing alkalinity by more than 1.0 dKH in a 24 hour period. Avoid calcium changes larger than 20 ppm per day. Rapid swings can stress coral tissue.
10. Reassess monthly. As corals grow and PAR increases, demand rises. Recheck consumption monthly by temporarily pausing auto dosing for 48 hours and measuring the daily drop again.

Kalkwasser Dosing: Simple, Powerful, pH Friendly

1. Confirm kalkwasser is appropriate. Kalk works best when your tank has moderate demand and a reliable ATO. It is also helpful if your pH dips at night because kalk raises pH.
2. Mix a safe starting concentration. Full saturation at room temperature is about 2 teaspoons of kalk powder per gallon of RO/DI. Start at 0.5-1 teaspoon per gallon so you can evaluate pH response and alkalinity rise.
3. Let it settle, use only the clear solution. Stir gently, then let the slurry settle for 30-60 minutes. Dose from the clear liquid above the fine white sediments. Keep the intake line 1-2 inches above the bottom.
4. Introduce kalk slowly. Begin by replacing 25-50 percent of your daily evaporation with kalkwasser, the rest with plain RO/DI. Increase weekly if alkalinity remains stable and pH stays within 7.8-8.4.
5. Prefer nighttime dosing. If possible, deliver more kalk when lights are off to support nighttime pH. A peristaltic pump on a timer that runs more at night can optimize this effect.
6. Track pH and alkalinity. If pH exceeds 8.4-8.5 or alkalinity rises more than 0.3 dKH per day, reduce the concentration or percentage of evaporation replaced with kalk.
7. Maintain the reservoir. Keep the container sealed to limit CO2 contact, which neutralizes kalk. Refill weekly and fully rinse the container monthly to remove calcium carbonate crusts.
8. Know kalk's limits. If your tank's demand exceeds what evaporation can deliver, supplement with two-part or switch to two-part completely. Do not spike kalk concentration to compensate because pH can climb too high.
9. Avoid risky additives. Only use vinegar or other carbon sources to increase kalk solubility if you clearly understand the side effects. For most hobbyists, it is better to stick with standard saturated kalk.
10. Safety first. Kalk is caustic. Wear gloves and glasses, avoid contact with skin and eyes, and keep powders and solutions away from children and pets.

Best Practices and Common Pitfalls

• Keep daily alkalinity swings within 0.2 dKH if possible. Stability beats chasing a perfect number.
• Calibrate dosing pumps every 1-2 months. Measure actual output in mL per minute with a graduated cylinder.
• Keep dosing lines separated and secured. Never let alkalinity and calcium solutions meet before they hit tank water.
• Use check valves or anti-siphon loops to prevent backflow into dosing containers.
• Do not dose near skimmer intakes or filter socks where precipitation could accumulate.
• Label containers and tubes clearly. Store chemicals sealed in a dry, cool place.
• Watch salinity. Two-part adds sodium and chloride over time, slowly increasing salinity. Verify SG weekly and perform water changes as needed to maintain 1.025-1.026.
• Replace test reagents before expiration and cross-check a new kit against the old to catch errors.
• Changes should be incremental. Increase or decrease dosing by 10-20 percent at a time, then re-test.
• Plan power-out contingencies. Pumps stopping overnight can allow parameters to drift. Stable dosing schedules and verified UPS backups reduce risk for sensitive SPS.

How Dosing Affects Water Parameters

Two-part dosing adds sodium carbonate or bicarbonate and calcium chloride. Over time, this gently increases sodium and chloride in the system, which is countered by normal water changes. Sodium carbonate tends to raise pH more than bicarbonate, which can be helpful if your pH is low, but do not allow pH to exceed about 8.4-8.5.

Kalkwasser adds both alkalinity and calcium in a balanced ratio while also consuming dissolved CO2, which increases pH. This is excellent for coral calcification but requires careful monitoring. Too much kalk can cause a fast pH rise, snowstorm precipitation, and a sudden drop in calcium and alkalinity afterward.

Magnesium plays a critical supporting role by inhibiting unwanted precipitation of calcium carbonate. If magnesium is low, you may see chronic difficulty keeping alkalinity and calcium stable. For a deep dive, see Magnesium in Reef Tanks: Complete Guide | Myreeflog.

As calcification increases, nutrient demand increases too. Faster-growing corals consume more nitrate and phosphate, which can cause bottoming out if you are not watching trends. Balanced nutrients support color and growth. Learn more here: Nitrate in Reef Tanks: Complete Guide | Myreeflog and Phosphate in Reef Tanks: Complete Guide | Myreeflog.

Scheduling and Tracking

Make dosing a routine that you can stick with. Consistency is what keeps parameters steady and corals happy.

• Daily or near-daily: check alkalinity while dialing in. Afterward, 2-3 times per week is fine for most tanks.
• Weekly: test calcium and magnesium, inspect dosing lines, check pump reservoirs, and verify salinity.
• Monthly: recalibrate pumps, clean dosing tube tips, and re-measure daily consumption to adjust your baseline.
• Quarterly: replace worn tubing and consider replacing probe solutions or test kit reagents.

Automated reminders and trend charts make this simple. My Reef Log lets you set recurring tasks for testing and maintenance, then overlay dosing amounts with alkalinity and calcium readings to confirm your settings are working. If you see a slow drift, you can adjust before it becomes a problem.

When you add new corals, change lighting intensity, or increase PAR, plan to recheck consumption. My Reef Log helps you capture those event notes beside your test data so the story behind every change is easy to see later.

Conclusion

Dosing is not just adding chemicals, it is a controlled process that matches your reef's natural consumption. Two-part dosing offers precision and flexibility, while kalkwasser adds a balanced boost and supports pH. Start with careful testing, move in small steps, and let stability guide your decisions. With My Reef Log organizing your tests, doses, and reminders, you can focus on coral health and enjoy predictable growth.

Frequently Asked Questions

Should I choose two-part or kalkwasser for my tank?

Use two-part if you want precise control or your tank has high demand that exceeds evaporation. Use kalkwasser if your demand is moderate and you would benefit from a pH lift, especially overnight. Many hobbyists start with kalkwasser and later supplement or switch to two-part as coral growth increases.

Can I use kalkwasser and two-part together?

Yes. A common approach is to run kalkwasser as your base, then use small amounts of two-part to make up any shortfall. Watch pH and avoid exceeding 8.4-8.5. Adjust slowly and test alkalinity frequently when changing the balance between the two methods.

What if my alkalinity keeps drifting even though I am dosing?

First verify test kit accuracy and check salinity. Re-measure daily consumption by pausing auto dosing for 48 hours and tracking the drop. If magnesium is low, correct it. Make sure dosing lines are not clogged and that your pump calibration is accurate. Increase or decrease your daily dose by 10-20 percent, then re-test after 24 hours.

Can I hand dose without pumps?

Yes, especially for lower-demand tanks. Dose small amounts once or twice per day rather than one large bolus. Add alkalinity in high flow, wait 10-15 minutes, then add calcium. As demand grows, a simple two-channel dosing pump improves stability and convenience.

How do I prepare for travel or a vacation?

Top off dosing containers, verify pump calibration, and ensure your ATO is reliable. Set conservative dosing amounts and ask a tank sitter to test alkalinity mid-trip rather than adjust dosing. Write clear instructions and keep emergency contact info handy.