Here's what I like to use
From Seachems site:
Reef Advantage Calcium™ is equivalent to dry Reef Complete™. It is a non-caustic (pH 8.3-8.6) optimized blend of ionic calcium designed to restore and maintain calcium levels found in natural seawater. Calcium and carbonates are essential to all coral growth. If either becomes deficient, coral growth will cease, followed by a rapid decline in coral health. Reef Advantage Calcium™ also includes magnesium and strontium in amounts proportionate to typical utilization ratios (100:5:0.1, Ca:Mg:Sr). This allows one to maintain these two important elements while maintaining calcium. Unlike limewater (kalkwasser), Reef Advantage Calcium™ does not have a caustic pH and will not deplete magnesium. Used as directed, it will not deplete alkalinity. A 500 g bottle treats 16,000 L (4,000 gallons).
Sizes: 100 g, 250 g, 500 g, 1 kg, 4 kg, 20 kg
DIRECTIONS: BEGINNER: Use 1 level teaspoon per 150 L (40 gallons) twice a week. Dissolve in at least one cup of freshwater. Check calcium every 2 weeks and adjust dose or frequency accordingly.
ADVANCED: Check calcium level, then follow dosing regimen above until calcium is adjusted to 380–420 mg/L. Each dose will raise calcium by about 12 mg/L. Size or frequency of dose can be adjusted, but do not exceed 25 mg/L per day. Thereafter, use as required to maintain calcium.
EXPERT: After determining the calcium consumption rate, set up a continuous drip system. Use the following formula to determine how much to add to your top-off water: t=0.002vc (t=teaspoons to add to top off water, v=volume of tank in gallons, c=amount to raise calcium in mg/L). For example, if you want to raise calcium by 25 mg/L in a 50 gallon tank, then you would add 0.002x50x25=2.5 teaspoons into the top-off water. HINTS: If used with Reef Calcium™, it is not necessary to exceed 380 mg/L total calcium. Use Reef Status™: Calcium to measure calcium.
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Reef Builder ™ raises carbonate alkalinity without immediately impacting on pH. With long term use there will be a tendency to stabilize at pH 8.3. Carbonates and calcium are essential to all coral growth. If either becomes deficient, coral growth will cease, followed by a rapid decline in coral health. Used as directed, Reef Builder™ will not deplete calcium, magnesium, or strontium which usually tend to precipitate with increasing alkalinity. Reef Builder™ and Reef Buffer™ may be used together. Use Reef Builder™ to raise carbonate alkalinity without affecting pH. Use Reef Buffer™ to raise carbonate alkalinity and pH. 500 g treats 32,000 L (8,000 gallons).
Sizes: 250 g, 500 g, 1 kg, 4 kg, 20 kg
DIRECTIONS: BEGINNER: Use half a level teaspoon per 150 L (40 gallons) twice a week. Dissolve in at least one cup of freshwater. Check alkalinity every 2 weeks and adjust dose or frequency accordingly.
ADVANCED: Check alkalinity, then follow dosing regimen above until alkalinity is adjusted to 4–5 meq/L. Each dose will raise alkalinity by about 0.25 meq/L. Size or frequency of dose can be adjusted, but do not exceed 1 meq/L per day. Thereafter, use as required to maintain alkalinity.
EXPERT: After determining the alkalinity consumption rate, set up a continuous drip system. Use the following formula to determine how much to add to your top-off water: t=0.05va (t=teaspoons to add to top off water, v=volume of tank in gallons, a=amount to raise alkalinity in meq/L). For example, if you want to raise your alkalinity by 1 meq/L in a 50 gallon tank, then you would add 0.05x50x1=2.5 teaspoons into the top-off water. HINTS: Use MultiTest:™ Marine pH & Alkalinity to measure total alkalinity./>
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Reef Buffer™ is intended primarily for use in a reef system where the maintenance of a pH of 8.3 is often difficult. When used as directed Reef Buffer™ will raise the pH of your reef system to 8.3 without fear of accidentally overshooting the pH to a dangerous level. Reef Buffer™ will also raise carbonate alkalinity. Reef Buffer™ is a blended product and is not just sodium carbonate. Reef Builder™ should be used to raise alkalinity when pH is not a problem. Use Seachem's MultiTest: Marine pH & Alkalinity™ to check pH and total alkalinity. 500 g treats 16,000 L (4,000 gallons).
Sizes: 250 g, 500 g, 1 kg, 4 kg, 20 kg
DIRECTIONS: Check pH and alkalinity before use. Use 5 g (1 level teaspoon) for every 150 L (40 gallons) to raise pH by about 0.1 pH units (this will also raise alkalinity by about 0.5 meq/L). Dissolve in at least one cup of freshwater, then add to the tank. The pH of natural sea water is 8.25–8.30. In a well established reef system pH adjustment may be necessary biweekly to semiweekly. Dosing requirements will vary, but do not exceed the recommended dose without checking your pH and alkalinity (alkalinity should not exceed 6 meq/L). If an alkalinity of 6 meq/L has been reached and a pH of at least 8.20 has not been attained or substantial cloudiness that does not clear within 15 minutes is encountered, then the system is not ionically balanced. To restore ionic balance perform a water change or adjust the magnesium and calcium levels to approximately 3:1 Mg:Ca (calcium does not need to exceed 400 mg/L). DO NOT OVERDOSE: Excess alkalinity may enhance the loss of calcium, magnesium, and strontium. Do not directly mix with any calcium, magnesium, or strontium supplement.
There are tons of products out there to use.
Most of them work okay once you get your usage/dosage dialed in.
I've settled in on these 3 as my primary - until I get a calcium reactor.
These 3 products - along with a 15-20% water exchange every 4-6 weeks is working well for me.
I like to mix powders with RO/DI top off water.
