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In reference to large water changes....)
In doing batch changes, aquarists should consider the changes in the water parameters that will result, and be sure they do not excessively stress organisms. Differences in salinity and temperature are most likely to be significant, and the larger the change, the more stressful it can become for the aquarium's inhabitants. If there is substantial ammonia in the new water, as there may be in
artificial salt water or possibly in natural seawater that has been stored for a while, that can also be stressful. Obviously, any organisms that become exposed to the air can also be greatly stressed. Differences in other water parameters are less likely, in my opinion, to be particularly stressful during water changes, with the possible exception of certain trace elements which may be more toxic in raw artificial seawater when not bound to
organics than after they have had a chance to become bound in the aquarium or in natural seawater. The normally encountered differences in calcium, magnesium, alkalinity, nitrate, phosphate, silica, pH, etc., are unlikely to unduly stress organisms during water changes up to 30-50% using natural seawater or aerated artificial seawater, in my opinion.