Can't give an exact answer to that question, because it's going to be different for every system, due to the differing demand for Alk, Ca and Mg. Yes, Mg too. The following things influence the rate of demand for Alk, Ca and Mg:
- type and amount of coral
- type of sand (need for dosing Ca and Mg is less in the presence of Utah Oolitic Sand)
- amount of sand (advantages of a DSB)
- type and amount of light (sunlight = fastest growth, MH lighting = next fastest growth)
- amount of Coralline Algae
- number of Snails(shell) and other inverts (shrimp/bugs/worms have calcareous exoskeleton/spines)
- number and size of fish (bone)
- level of Alk within the range (there is a sweet spot
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)
Also note;
When a hobbyist first starts seeing that the demand for Alk and Ca has exceeded what Kalkwasser can deliver, manual dosing once or twice every 10 days is sufficient to bring the levels back up within range so that Kalk can continue to deliver most of the needed Alk and Ca. At this point there is no need to fret about keeping Alk and Ca at exact numbers every day. The "stability" you may have read about can be ensured by simply keeping these within range on a weekly basis. (Alk 8-12 dKH; Ca 350-500 ppm)
The demand for Mg is slower and can be satisfied by once/month additions. It's okay to raise Mg to something like ~1500 ppm and not dose again until it has dropped to ~1200 ppm.
For me, when the system requires manual dosing more often than bi-weekly, that's when automatic dosing becomes convenient.
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Your need may differ.
The question eventually comes up, how much to dose? The simple yet IMO most useful answer is to test, dose a little and test again the next day. Following that result, increase or decrease the amount and/or timing of the next dosing accordingly. Testing is an important key to success.
Aloha,
Mark
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Edited by Mark Peterson - January 25 2016 at 5:44am