Dosing Checklist for Reef Keeping

Alkalinity can swing noticeably over a 24-hour period, especially in SPS systems and tanks using kalkwasser. Measure dKH at a consistent time to identify true daily consumption before setting any dose.

Confirm calcium is in a reasonable reef range, typically 380-450 ppm, before relying on automated dosing. If calcium is already far out of range, correct it manually first instead of expecting a doser to catch up safely.

Low magnesium can make calcium and alkalinity harder to keep stable by increasing unwanted precipitation. Test magnesium before troubleshooting inconsistent two-part consumption or kalk deposits on heaters and pumps.

Target 1.025-1.026 SG at 77 F, because inaccurate salinity skews calcium, alkalinity, and magnesium readings. Calibrate with 35 ppt solution, not RO water, for reef-level accuracy.

Kalkwasser raises pH and is often used specifically to combat low pH, so you need to know your tank's real day-night range before using it aggressively. Many reef tanks run around 7.8-8.4, and large spikes above that can stress livestock.

If alkalinity drops from 8.3 to 7.8 dKH in 24 hours, your system is consuming about 0.5 dKH per day. That number is the most useful starting point for calculating two-part dosing volume.

Two-part is usually the easiest option for tanks with growing LPS and SPS colonies because calcium and alkalinity can be adjusted independently. It works well when demand is too high for water changes alone to maintain stability.

Kalkwasser dosing depends on top-off volume, so it is best suited to systems with predictable daily evaporation. Seasonal humidity shifts can change how much kalk enters the tank, which can alter alkalinity and pH unexpectedly.

Heavy SPS systems often consume more alkalinity and calcium than saturated kalk can deliver through normal evaporation. In those tanks, kalk is often paired with two-part or a calcium reactor instead of used by itself.

Two-part additives can crust around lids and tubing exits, especially alkalinity solutions. Use sealed reservoirs and inspect them regularly so concentration stays consistent and contamination is minimized.

Frequent micro-doses are safer than one or two large additions, especially for alkalinity. A doser that can split the daily total into 8-24 doses helps reduce pH swings and local precipitation.

If the two solutions enter the sump too close together, they can react immediately and form calcium carbonate precipitate. Dose them into high-flow areas several minutes apart to preserve the additive strength.

If alkalinity is 6.0 dKH or calcium is 320 ppm, raise them gradually into target range before setting a maintenance dose. Dosing pumps are for replacing daily consumption, not for making large corrections quickly.

A conservative starting point reduces the chance of overshooting alkalinity in a tank with variable uptake. Re-test after 2-3 days and adjust based on actual trend rather than the calculator alone.

Fully saturated kalkwasser is commonly around 2 teaspoons of calcium hydroxide per gallon of RO or DI water, but product guidance should be followed. Let the slurry settle and dose only the clear solution, not the undissolved sediment.

A stuck float switch or failed optical sensor can dump high-pH kalkwasser rapidly and cause a major livestock emergency. Redundant ATO sensors and pump run-time limits make this method much safer.

Good flow helps additives disperse quickly and prevents concentrated solution from contacting probes, heaters, or ATO sensors. This reduces false readings, precipitation, and crust buildup around equipment.

Spacing the doses lowers the risk of the two parts mixing before they dilute into the system water. This is especially important in smaller sumps where water volume around the dosing outlet is limited.

Corals generally respond better to stable alkalinity than to chasing an exact number. Whether you run 7.5 dKH or 8.5 dKH, keeping it consistent is more important than frequent large adjustments.

Calcium usually moves more slowly than alkalinity, so weekly checks are often enough once the tank is stable. If calcium keeps drifting despite steady alkalinity, check doser calibration and solution concentration.

Magnesium is consumed more slowly, but neglecting it can make dosing seem inconsistent over time. Tanks with heavy coralline algae growth and frequent skeleton-building coral growth can still pull magnesium down steadily.

Large changes make it harder to identify the real effect and can shock sensitive corals. A measured adjustment followed by 2-3 days of testing is a more reliable way to dial in consumption.

If pH regularly climbs above about 8.45 after dosing, back off and reassess delivery rate, aeration, and total kalk input. High pH events can trigger precipitation and stress fish, corals, and invertebrates.

New Acropora growth, plating Montipora expansion, and Tridacna clams can materially increase calcium and alkalinity uptake in a short time. Do not assume last month's dosing schedule will still hold after stocking changes.

Peristaltic tubing wears over time and can change the actual delivered volume. A pump programmed for 20 mL may no longer deliver 20 mL accurately, which creates creeping instability that is easy to miss.

Alkalinity solutions are notorious for forming crust at the line tip, especially near warm, high-airflow sump areas. A partial clog can reduce dose output without triggering any equipment alarm.

Excess sediment and impurities can reduce consistency and foul moving parts or sensors. Periodic cleaning keeps kalk concentration more predictable and reduces pump wear.

Testing error, reagent age, or sample contamination can lead to unnecessary corrections. If a result looks out of character, repeat the test before raising or lowering your dose significantly.

White crusty buildup often means additives are being dosed too fast, too close together, or into an area with poor flow. Precipitation wastes calcium and alkalinity and can lower pump efficiency over time.

Rapid alk swings can stress SPS, particularly Acropora, even if the final value falls within an acceptable range. Review test records, verify doser output, and return to stability rather than making more aggressive corrections.