Switching from hand-dosing to an automated dosing pump is one of the highest-impact upgrades you can make for a reef tank. Not because it saves time — though it does — but because no human can match a pump's consistency. Corals do not care about your schedule, your weekend plans, or the fact that you forgot. They calcify continuously, consuming alkalinity and calcium around the clock at a remarkably steady rate. The closer you can match your dosing to that consumption rate, the faster and more uniformly your corals grow, and the fewer unexplained losses you will experience. This calculator takes your total daily dose and turns it into a precise, precipitation-safe schedule optimised for your specific pump configuration.
Who Should Use This Calculator
This tool is for reef tank keepers who already know their daily alkalinity, calcium, and magnesium consumption — either calculated from a two-part dosing calculator or measured empirically through consumption testing — and need to translate those volumes into an actual pump programming schedule. It is especially valuable for reefers who are new to automated dosing and unsure how to space their pumps safely, those who have experienced a precipitation event (the white snowstorm) and want to prevent it from happening again, and experienced hobbyists setting up a new dosing system who want an optimised schedule rather than a rough manual estimate. If you do not yet know your daily dose, use the Reef Two-Part Dosing Calculator first and return here once you have your daily volumes.
The Danger of Precipitation — What Causes the Snowstorm
Alkalinity supplements — whether you are using sodium carbonate (soda ash), sodium bicarbonate, or the alkalinity component of a commercial two-part solution — are highly concentrated and have an extremely elevated pH, often above 11 to 12. Calcium supplements — calcium chloride or the calcium component of two-part — are also highly concentrated. Reef water is already at the thermodynamic edge of calcium carbonate saturation; that is simply what a healthy reef chemistry looks like. When you add a concentrated bolus of alkalinity into water that simultaneously receives a concentrated bolus of calcium, the localised chemistry in that mixing zone becomes so far outside equilibrium that calcium and carbonate ions instantly crystallise out of solution as solid calcium carbonate — white, fluffy, biologically useless precipitate.
This precipitation does several things simultaneously: it wastes the supplements you just added (you paid for them and they are now gravel), it lowers both alkalinity and calcium in the water faster than the corals removed them, it can clog dosing pump lines and sump equipment, and if it happens repeatedly, it creates false confidence that you are dosing correctly while your corals are actually being starved. The fix is architectural — never allow concentrated alkalinity and calcium solutions to mix before they have been diluted by the full volume of your system.
The Logic of Staggering Your Pumps
The standard and universally recommended approach is to alternate alkalinity and calcium doses so that each supplement has time to disperse through the full water volume before the other is introduced. A minimum gap of 15 minutes is often cited, but 30 minutes is safer and 60 minutes is better still for large doses in small sumps with slow circulation. The classic schedule runs alkalinity at the top of each hour and calcium at the half hour — or vice versa. The direction does not matter; what matters is the consistent gap. If you add magnesium as a third component, it can be dosed at a quarter-hour interval or, since magnesium changes slowly and is consumed in smaller relative quantities, once or twice per day at a time isolated from both other pumps.
Where your tubes discharge into the sump also matters. Ideally, alkalinity and calcium lines should enter the water at different physical locations — opposite ends of the sump, or one into the return section and one into the refugium — and both should discharge into high-flow areas so the concentrated solution is swept away and diluted as quickly as possible.
Why Micro-Dosing Beats Large Single Doses
Imagine your tank needs 100 ml of alkalinity per day. You could dose it all at once — one big pump run at midnight. Your alkalinity would spike sharply at midnight, then slowly decline all day as corals consume it, reaching its lowest point just before the next dose. That daily swing — from high to low and back again — creates a measurable fluctuation in both alkalinity and pH that corals experience as instability. It does not necessarily kill them, but it slows growth, reduces polyp extension, and in sensitive SPS species can contribute to browning, STN (slow tissue necrosis), and RTN (rapid tissue necrosis).
Now divide that same 100 ml into 24 doses of approximately 4 ml each, one per hour. Your alkalinity now varies by such a small margin between doses that a sensitive test kit can barely detect the difference. pH fluctuation from dosing is similarly flattened. Corals receive a constant, even supply of the ions they need rather than a feast-and-fast cycle. The result — consistently reported across the reef-keeping community — is visibly faster and more symmetrical growth, better polyp extension during daytime, and a much more forgiving system if you occasionally miss a dose by a few hours. Micro-dosing is not optional for serious SPS keeping — it is the minimum standard.
Using Alkalinity Dosing to Manage Nightly pH Drops
In a mature reef tank with significant coral mass and a macroalgae refugium, pH follows a predictable daily cycle. During the light period, photosynthesis by corals, coralline algae, and refugium macroalgae consumes CO2 from the water, raising pH — sometimes as high as 8.4 to 8.5. When the lights go off at night, photosynthesis stops but respiration continues; CO2 accumulates, carbonic acid forms, and pH drops — sometimes falling below 8.0 by early morning. This nightly pH trough is a real stressor for corals and calcification slows at lower pH.
Because sodium carbonate (soda ash) is highly alkaline and actively raises pH when dosed, many experienced reefers program their alkalinity pump to dose exclusively or predominantly at night — during the hours when pH is naturally falling. This strategically counteracts the nightly drop and keeps the pH range tighter across the full 24-hour cycle. This calculator includes an option to weight your alkalinity micro-dose schedule toward night hours while keeping calcium dosing balanced across the full day, achieving both precipitation safety and pH management simultaneously.
Calibrating Your Dosing Pump Accurately
All dosing pump schedules are only as accurate as the pump calibration. Most hobbyist peristaltic dosing pumps — Jebao, BRS, Neptune DOS, Kamoer, and similar — have a nominal flow rate stated in the manual, but the actual rate can vary by 5 to 20% from the specification due to tube wear, head pressure, and manufacturing variance. Before programming any schedule, physically calibrate your pump: run it for a fixed time (60 seconds is practical), collect the output in a graduated cylinder, and calculate the actual ml per minute. Re-calibrate every three to six months, and any time you replace the tubing. An uncalibrated pump on a tight dosing schedule is not precise dosing — it is approximate dosing with a false sense of precision.
When to Reassess and Update Your Schedule
Your dosing requirements are not static. As corals grow, their calcification demand increases — a frag-dominated tank today may have three to five times the calcium and alkalinity consumption in 18 months when those frags have grown into colonies. Test alkalinity and calcium weekly (daily if you are keeping demanding SPS species), and update your daily dose volumes and pump schedule every four to six weeks as the tank matures. A dosing schedule that was perfect six months ago may now be falling significantly short, which will appear as corals losing colour, slowing growth, or developing tissue recession from the base. The calculator makes it simple to re-enter updated volumes and generate a revised schedule whenever your consumption changes.