All my other perimeters will be sustained by a 2 gallon change DALIY.
I agree that you will be unlikely to be able to maintain alkalinity with 2 gallons per day. Maybe 20-50 gallons per day would do it. I show that here:
Water Changes in Reef Aquaria
http://reefkeeping.com/issues/2005-10/rhf/index.php
from it:
http://reefkeeping.com/issues/2005-10/rhf/index.php#8
Very Large Water Changes Maintain Calcium and Alkalinity
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In the previous section I showed that normal water changes of up to 30% per month cannot maintain calcium and alkalinity in reef aquaria. But at some point, large enough water changes can do so. What volume of water change is necessary to maintain calcium and alkalinity in reef aquaria? In a tiny aquarium, 3 gallons for example, large daily water changes might be acceptable. How large is required? Figure 23 shows the drop in alkalinity for a low demand aquarium changing 0%, 5%, 10%, 15% and 30% of the water EVERY DAY. In that case, it appears to require between 10% and 30% of the total water volume to be changed every day to maintain suitable alkalinity. Figure 24 shows similar data for a higher demand aquarium (1 meq/L alkalinity per day). In this case, it takes close to a 50% water change each day to maintain suitable alkalinity. Similar data are obtained for calcium (not shown), where 30% and 50% daily water changes in a high demand aquarium (24 ppm calcium per day) stabilize at 364 and 396 ppm calcium, respectively. So, while changing 50% per day is really out of the question for any normal to large reef aquarium without an inlet directly from the ocean or a large seawater well, a 3-gallon nanoreef aquarium attached to a very slow continuous pump could maintain adequate calcium and alkalinity by replacing 1.5 gallons each day.
Figure 23. Alkalinity as a function of time when performing very large daily water changes of 0% (no changes), 5%, 10%, 15% and 30% of the total volume EACH DAY. In this example, alkalinity is present at 4 meq/L (11 dKH) at the start and is depleted at a low rate of 0.2 meq/L per day.
Figure 24. Alkalinity as a function of time when performing very large daily water changes of 0% (no changes), 15%, 30% and 50% of the total volume EACH DAY. In this example, alkalinity is present at 4 meq/L (11 dKH) at the start and is depleted at a moderately high rate of 1 meq/L per day.
