Supplementation and Calcification Support

Giant clams, stony corals and coralline algae build their shells and skeletons from calcium carbonate they take out of the water (Modules 3 and 6). Every day they pull calcium and carbonate out, and alkalinity falls with it. Giant clams need calcium and alkalinity at the right level.

Water changes put some back, but in a system full of growing calcifiers, demand outruns water changes; calcifiers using more than is added is the most common calcium and alkalinity problem. Calcium, alkalinity and magnesium are used in by far the largest amounts, so they're the main supplements; other elements are used in tiny amounts (section 14). Demand grows as the animals grow, so a dose that was right last month can be short this month.

Alkalinity can sit anywhere from 6 to 10 dKH, but IMARCS prefers 7.5 to 8.5; lower nutrient levels generally need lower alkalinity. Stable but non-ideal numbers are far less harmful than chasing numbers and causing swings.

Calcifiers remove calcium and alkalinity together: alkalinity drops about 1 meq/L (2.8 dKH) for every 20 ppm of calcium removed. A balanced supplement adds them back in about that ratio. Magnesium keeps calcium carbonate from coming out of the water on its own (Module 6); about 1,300 ppm helps prevent that.

Other parameters move them too. When phosphate rises, calcification slows, so the animals use less alkalinity; with the same dose, alkalinity climbs. When pH rises, alkalinity drops faster. Higher pH and higher alkalinity both increase demand. Overdose a balanced supplement and much of the excess comes out as calcium carbonate crust on heaters and pump impellers.

Alkalinity shows a dose change within a few days; calcium changes slowly, so alkalinity is the test that guides dosing. Test at the same time each day with the same instrument, and log it (Module 7). A reading far off the last one, or one that makes no physical sense, is retested before it's recorded; a second test kit, ideally another brand, confirms a surprising result.

Start with the product's suggested dose, or a little less, since starting low is easier to correct. Check alkalinity after 2 to 3 days, adjust, and repeat until alkalinity stays in range. Expect 2 to 4 weeks of adjustments, testing daily at first. If alkalinity falls a steady amount each day on the same dose, the dose is short by that amount. If it climbs, either the dose is too high or demand has dropped; check phosphate before cutting the dose (section 2).

Use the system's real water volume: tank plus sump, minus rock and sand (Module 36). Product strength comes from the label: on Red Sea's Reef Foundation B, for example, 1 mL raises 100 L (about 25 US gallons) by about 1 dKH. Alkalinity is given in dKH or meq/L; 1 meq/L is about 2.8 dKH (Module 6).

Worked example: a 300 L system on that product loses 0.2 dKH a day more than it gets. Extra dose = 0.2 x 300 / 100 = 0.6 mL a day. Baking soda works the same way: about 16 g raises 190 L (50 US gallons) by 1 meq/L. Raise or lower a dose in small steps, one change at a time (Module 1).

Kalkwasser (German for limewater) is calcium hydroxide (hydrated lime) or calcium oxide (quicklime) dissolved in fresh water. It's always made with RO water; mixed with sea water it precipitates. Saturated limewater at 25 C (77 F) holds about 808 ppm calcium and 40.8 meq/L (about 114 dKH) of alkalinity, at about pH 12.5. The hydroxide raises pH and reacts with carbon dioxide, which helps systems with excess CO2 from a calcium reactor or the room air.

Dose it slowly and continuously as top-off water, by a dripper or a slow pump, often controlled by a float switch. Let it settle a few hours to overnight and draw only the clear water. Leave the solids on the bottom (they bind some metals) and discard them once they discolor or after 6 to 12 months. Air turns limewater into insoluble calcium carbonate, so keep the reservoir lidded and never aerate it. Don't mix other supplements into it.

How much it can add is capped by evaporation. Worked example: a 400 L system that evaporates 4 L a day of saturated limewater gets about 4 x 40.8 / 400 = 0.41 meq/L (about 1.1 dKH) a day. If demand is higher, it needs a second method. Limewater adds almost no magnesium, so magnesium slowly falls.

Added all at once, saturated limewater at 1.25% of the tank volume raises pH by 0.6 to 0.7; at 0.25% it raises pH 0.1 to 0.2. An overdose can turn the water milky white as calcium carbonate forms. If limewater feeds through the top-off and the top-off sticks on (Module 13), it keeps pumping limewater in, so the top-off's safety checks matter twice as much.

Fixing an overdose: if pH is 8.5 or lower, wait a few days; the precipitate dissolves and a water change usually isn't needed. Test alkalinity and calcium only after the water clears. If pH is above 8.5, bring it down only to about 8.5: carbon dioxide first (about 5 mL of soda water per 3.8 L, 1 teaspoon per US gallon, lowers pH a couple of tenths), then vinegar with strong aeration; acid only with live pH monitoring.

Handling lime: quicklime gets very hot when water is added and can boil it, so add a small amount of lime to a much larger volume of water. Don't breathe the dust or get it on skin or in eyes; rinse with plenty of tap water and get medical help for an eye splash.

A two-part system has a calcium part (calcium chloride) and an alkalinity part (bicarbonate or carbonate). They're kept in separate containers and never mixed. Dose equal amounts unless testing shows otherwise, into a high-flow area, with the two parts at different times; Red Sea's ReefDose adds a delay between heads so supplements don't react. Smaller doses more often keep levels steadier. Two-part suits small systems, systems without a top-off and any level of demand.

Commercial versions include Red Sea Reef Foundation and BRS Pharma. A widely used homemade recipe uses 500 g calcium chloride dihydrate per 3.8 L (1 US gallon) of RO water, about 37,000 ppm calcium, and 594 g baking soda baked at 150 C (300 F) for 1 hour per 3.8 L, about 1,900 meq/L. Baking turns baking soda into sodium carbonate, which raises pH more: about 0.15 to 0.35 per 0.5 meq/L added. For systems already above about pH 8.3, the same recipe uses unbaked baking soda instead, at half strength. Anhydrous calcium chloride needs about 20% less and gets very hot as it dissolves.

Homemade two-part isn't perfectly balanced: over time sulfate rises and some other ions fall, so test calcium, alkalinity and magnesium periodically. Water changes reset the balance.

Raising calcium 120 ppm with a balanced supplement would also raise alkalinity about 6 meq/L (about 17 dKH), so it can't correct one side alone. Use a single-part fix:

• Alkalinity high, calcium low: calcium chloride alone.
• Calcium high, alkalinity low: baking soda if pH is 8.2 or higher, washing soda if it's lower. A level teaspoon of baking soda (just under 6 g) raises 190 L (50 US gallons) about 0.4 meq/L (about 1 dKH).
• Both low: more of the balanced supplement.

Before any big correction, confirm the reading with a second instrument, and aim for the middle of the range. Don't add alkalinity to fix pH if alkalinity is already fine. A large imbalance can also be reset with water changes. If alkalinity is climbing on an unchanged dose, test phosphate first: rising phosphate slows calcification.

Fauna Marin's Balling Light uses three 5 L containers: calcium (2 kg calcium mix plus 25 mL each of trace 1 and trace 2), magnesium (2 kg magnesium mix, nothing else added) and carbonate (500 g carbonate mix plus 25 mL of trace 3). Its reference: 10 mL per 100 L raises alkalinity 0.5 dKH, calcium 11 mg/L and magnesium 5 mg/L.

Dose by pump with at least three heads, or by hand into a high-flow area: magnesium, then calcium, then carbonate, at least 2 to 3 minutes apart. Calcium salt heats the water as it dissolves; always add the salts to the water, never the other way around. Dose toward your system's own targets (section 2), and expect 2 to 4 weeks of adjustment with daily tests at first.

Tropic Marin's All-For-Reef is a one-part supplement: calcium, alkalinity (carbonate hardness), magnesium, strontium and trace elements in one solution; the powder version uses organic calcium salts. It's made not to change salinity or ion balance. The powder version is mixed at about 160 g per 1 L of RO water. IMARCS uses All-For-Reef exclusively, dosed by pump, whatever the system's size or demand, and sets the dose by alkalinity demand.

The All-For-Reef schedule: start at 5 mL per 100 L a day; each week raise it by 2.5 mL per 100 L while watching carbonate hardness, until it holds steady in range; never exceed 25 mL per 100 L a day. For a 300 L system that's 15 mL a day to start and 75 mL a day at most. The maximum is far above what most systems use: IMARCS systems holding coral colonies over 60 cm (24 in) and giant clams over 35 cm (14 in) don't come close to it. Because the ratio is fixed, it can't correct calcium or alkalinity alone; use a single-part fix (section 8). With no calcifiers to use it, it only raises the levels.

Calcium carbonate media only dissolves in acidic water. CO2 bubbled into the reaction chamber forms carbonic acid and lowers the pH; the media dissolves into calcium and bicarbonate, and the effluent carries them to the sump. The parts are the reaction chamber, feed pump, circulation pump, effluent valve, and a CO2 cylinder with regulator, needle valve, solenoid and bubble counter. A pH controller opens and closes the solenoid to hold the chamber's pH.

Use chunky media; fine media turns to mud. A common fill is about 90 to 95% full, with a 9 to 1 mix of calcium media and magnesium media, because calcium media alone can be low in magnesium. Effluent is typically 25 to 40 dKH. A reactor costs more to set up, can meet any demand if sized right, and needs little daily attention.

The effluent carries dissolved CO2, which can lower the display's pH. Dripping it into a refugium or algae reactor lets the CO2 off-gas, and kalkwasser at night offsets it. A second media chamber raises effluent pH only a few hundredths, though it does raise effluent alkalinity.

To tune it, run the feed fast for 24 hours to fill the reactor and purge air, then slow it to about 3 to 5 mL a minute (1 to 2 drops a second). Set the pH controller between 6.3 and 6.8, most often 6.5, or as the media maker says. Set CO2 to about 1 to 2 bubbles a second; the solenoid should be open most of the time. The pH usually settles within about an hour.

Then test calcium and alkalinity daily. If they fall, raise the flow; if they rise, lower it; one small change per 24 hours (for example, 10 to 15 mL a minute). It's tuned when results hold for 3 to 5 days in a row. Hold the pH steady and match demand with the flow. The pH probe in the reactor is calibrated like any other (Module 7); a drifting probe changes the whole output.

Natural sea water holds about 1,285 ppm; 1,250 to 1,350 is the preferred range. Low magnesium lets calcium and alkalinity come out of the water as calcium carbonate, so they become hard to hold. Check it regularly, and always when calcium and alkalinity are hard to maintain.

Coralline algae and other calcifiers use it, limewater adds almost none, and some reactor media are low in it. Water changes restore it. Supplements include commercial magnesium products, the magnesium part of a Balling system, and magnesium chloride with magnesium sulfate (Epsom salt). Magnesium sulfate adds sulfate, so add a small portion first the first time. Raise it no more than 50 to 100 ppm a day.

Trace elements are used in tiny amounts, and food and water changes bring many of them in. The rule is to know what you're adding and why. Mixtures of unknown content add things you can't measure, some potentially toxic, so they're avoided. When a test shows one element is short, dose it with a single additive of known strength; for example, strontium is dosed only when it tests below 5 ppm, to bring it to 5 to 15 ppm. Iron (chelated) is for macroalgae that are short of it. Iodine test kits detect only some of its forms, so dosing iodine to a test reading is unreliable.

All-For-Reef and Balling Light carry their traces in measured amounts inside the calcium and carbonate doses, so traces go in as the system uses calcium and alkalinity; Balling Light sets its trace amounts by how heavily stocked the system is. An ICP test (Module 7) shows what's really in the water. Water changes put back whatever the salt mix carries.

Most aquarium dosing pumps are peristaltic: rollers squeeze a soft tube and push liquid along it. Calibrate at the speed the pump will run, measuring into a container with exact markings, then check it with a test dose long enough for the pump to run at least a minute; repeat if it's off. IMARCS uses a 50 mL graduated cup with 5 mL marks and a small compartment marked in 1 mL steps up to 5 mL. Recalibrate after changing a tube.

For accuracy, keep lines as short and thin as practical; keep the containers below the water level so nothing siphons; never let the outlet hang in the water; a check valve helps only when the container sits below the water. Slow speeds are more precise for small doses. Red Sea's ReefDose, for example, doses 0.2 to 1,000 mL a day to ±0.05 mL, schedules hourly, delays between heads, tracks container volume and alerts on missed doses. Pump types and their apps are covered in Module 20.

Dosing lines can clog at the ends with precipitate, or burst along the way, so the liquid never reaches the system. The container level is one part of checking, not proof the dose is working. A clogged tip lets less through; a split line empties the container onto the cabinet floor.

Checks: watch a dose arrive at the outlet (most pumps have a prime or manual dose button); run a test dose into the graduated cup; compare the container drop with the schedule; follow each line for crust, kinks, splits and salt trails; make sure each line sits in its own container. Fixes: soak a crusted tip in hot water or hot citric acid water, and trim it back to clean tube if necessary; replace a split line; recalibrate after changing a pump tube.

Limewater suits systems with a top-off but can't be the only supplement for very high demand; two-part suits any size and demand and is cheap made at home; a reactor costs more but meets any demand with little daily work. Balling needs three pump heads and covers magnesium and traces; All-For-Reef is one bottle and works on any size of system and any demand; it's what IMARCS uses.

Methods combine. Kalkwasser at night offsets a reactor's CO2. Two-part can top up limewater when evaporation is low. Whatever the method, change one thing at a time (Module 1), log the results, and keep the numbers stable rather than chasing ideal ones.