Reef Dosing Schedule Guide: Calcium, Alkalinity, and Magnesium Timing

Most alkalinity swings that crash reef tanks come not from the dose itself but from when and how fast it lands. This reef dosing schedule guide shows you how to split and time your two-part dosing so chemistry stays flat rather than zig-zagging through the day. Based on fifteen years of commissioning SPS-heavy reefs at Gensou Aquascaping in Everton Park, we have refined a scheduling approach that works reliably in Singapore conditions where tanks run hot and coral demand climbs fast. Get this right and you remove one of the biggest causes of tissue necrosis.

Why Timing Matters More Than Dose

A 40 ml daily dose of alkalinity delivered in one hit swings dKH by roughly 0.5 or more in a 200 litre reef. Split across 24 smaller doses, the same total leaves dKH readings essentially flat. SPS corals, particularly Acropora, hate swings more than they hate mildly off-target values. The entire purpose of a dosing pump is to convert a manual plunge into a drip feed. If you are not splitting doses into at least ten increments, you are underusing your equipment.

Measuring Demand Before Scheduling

Before programming pumps, measure calcium, alkalinity, and magnesium three days running at the same hour. The daily drop is your consumption. A growing reef might consume 1.5 dKH, 20 ppm calcium, and 10 ppm magnesium per day. Match additive dose volume to replace exactly that loss. Overdosing because you want corals to grow faster is the fastest route to burnt tips.

Retest weekly for the first month, then every two weeks once readings stabilise. Hanna checkers for alkalinity and Salifert for calcium and magnesium are the Singapore standard, available at most LFS on Pasir Ris Farmway.

Calcium and Alkalinity Separation

Never dose calcium and alkalinity simultaneously into the same spot. When the two concentrates mix undiluted they precipitate as calcium carbonate snow, wasting reagent and fouling pump lines. Stagger them by at least 30 minutes and dose into areas of strong flow, typically the return chamber of the sump or directly in front of a powerhead. Some dosers allow you to set identical schedules offset by 30 minutes, which is the cleanest approach.

A Practical 24-Dose Schedule

For most mixed reefs, 24 doses of alkalinity per day spaced hourly works beautifully. Calcium runs on the same hourly cadence but offset by 30 minutes. Magnesium, which is consumed far more slowly, can drop in a single daily dose at 3 am when no other supplements run. The pattern looks like: alkalinity at the top of every hour, calcium at the half hour, magnesium once nightly.

If you use trace element supplements or amino acids, schedule them midday when lights are at peak intensity and corals are actively feeding. Avoid dumping traces into the dark hours when uptake is minimal.

Night versus Day Dosing

pH drops overnight as corals and bacteria respire without photosynthesis offsetting them. Adding alkalinity during those low-pH hours helps buffer the natural swing. If your dKH readings show a dawn dip, weight the schedule slightly toward the 8 pm to 6 am window. A 60/40 night bias often smooths out morning lethargy in SPS colonies.

Pump Selection and Local Pricing

Kamoer FX-STP, Jebao DP-4, and Neptune DOS dominate the Singapore market. Kamoer four-head units sell for about 280 to 380 SGD at Iwarna Aquafarm and Reef Systems, while the Neptune DOS runs around 650 SGD but integrates natively with Apex. For a starter two-part setup, four heads is the sweet spot: two for the main elements and two for future additions such as trace blends or vinegar.

Singapore Water and Tropical Drift

PUB tap water is soft with low carbonate hardness, so even top-up through an ATO reservoir drifts tank alkalinity downward during evaporation. Use RODI for both top-up and dosing dilutions to eliminate this slow drift. Tropical room temperatures of 30 degrees also speed chemical uptake and bacterial metabolism, so expect consumption rates roughly 10 to 15 per cent higher than equivalent tanks in temperate climates.

Related Reading

• Two Part Dosing Guide
• Balling Method Reef Dosing
• Best Dosing Pumps for Reef Tanks
• Best Reef Dosing Container Setup
• Calcium and Alkalinity Stability

Conclusion

Reliable dosing is a solved problem once you measure demand, split doses hourly, separate calcium from alkalinity, and use RODI dilutions. Programme the pumps, log your tests, and let the schedule run quietly in the background. For tailored dosing plans and pump commissioning in Singapore, the team at Gensou Aquascaping at 5 Everton Park is happy to walk through your numbers.