Reef dosing keeps key elements stable as corals grow. It replaces what your tank consumes each day. This guide helps you dose with confidence and avoid common mistakes.
Start with testing and a simple plan
Test first and dose second. Always measure alkalinity, calcium, and magnesium. Use reliable kits and log results. Test at the same time daily for one week.
Target stable reef ranges. Keep alkalinity at 7.5–9.0 dKH for most mixed reefs. Keep calcium at 400–450 ppm. Keep magnesium at 1250–1400 ppm. Stability matters more than chasing a perfect number.
Calculate daily consumption with two tests. Test alkalinity today, then again 24 hours later. Do not dose between those tests. If alkalinity drops 0.5 dKH, that is your daily demand. Repeat for calcium every few days.
Start low and ramp up. Dose 50% of the calculated daily need for three days. Re-test and adjust. This reduces overshoots and cloudy water. For setup basics, review reef tank parameters.
- Test alkalinity daily until it stays within 0.2 dKH.
- Adjust doses by 10–15% at a time.
- Recheck salinity weekly at 1.025–1.026 SG.
Choose a dosing method and dose safely
Two-part dosing is the most common approach. It adds alkalinity and calcium in balanced amounts. Many tanks also need magnesium occasionally. Dose alkalinity and calcium at least 10 minutes apart.
Use a dosing pump for consistency. Split the daily dose into 4–24 small doses. This reduces pH swings and precipitation. A good starting schedule is 8 doses per day. Dose into a high-flow area in the sump.
Limit how fast you correct alkalinity. Do not raise more than 1.0 dKH per day. Fast jumps can stress SPS corals. Calcium can rise 20–30 ppm per day safely. Magnesium can rise 50 ppm per day.
Watch pH when dosing alkalinity. Soda ash can raise pH quickly. Baking soda has a smaller effect. If your pH runs 7.8–8.0, soda ash may help. If your pH runs 8.3, use baking soda instead. For equipment tuning, see dosing pump setup.
- Label dosing containers and lines to avoid mix-ups.
- Calibrate pumps monthly using a measuring cup and timer.
- Never dose alkalinity and calcium into the same spot.
Trace elements, nutrients, and troubleshooting
Trace dosing is optional for many tanks. Start with water changes and stable major elements. If you dose traces, use a measured system. Dose based on consumption or ICP results. Avoid “more is better” thinking.
Nutrients affect dosing needs. Low nitrate and phosphate can slow coral growth. That can reduce alkalinity demand. Aim for nitrate 2–15 ppm and phosphate 0.03–0.10 ppm in many reefs. Adjust feeding before adding extra supplements.
Cloudy water after dosing often means precipitation. This can happen with high pH and high alkalinity. It also happens when dosing into low flow. Stop dosing for a few hours and test alkalinity. Resume at a lower dose and improve flow.
A real-world example helps. A 75-gallon mixed reef drops from 8.5 to 8.0 dKH in 24 hours. That is 0.5 dKH daily demand. The aquarist doses alkalinity in 8 parts across the day. After one week, the tank holds 8.3–8.5 dKH. Coral tips stay bright and polyp extension improves. For nutrient balance, read nitrate and phosphate in reefs.
- If alkalinity rises but calcium falls, your dosing is unbalanced.
- If both rise, you are overdosing or testing incorrectly.
- If both fall, increase dose by 10% and re-test in 48 hours.
Reef dosing works best with patience and records. Test, dose small amounts, and adjust slowly. Stable alkalinity and nutrients will reward you with better growth and color.
Sources: Randy Holmes-Farley, “An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System” (Reefkeeping Magazine); Randy Holmes-Farley, “Alkalinity” (Reefkeeping Magazine); Julian Sprung, The Reef Aquarium, Vol. 1–3.
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