I think that if your usinging it during water changes you'll be fine as you are basically doing a slow switch over like that anyway. I also can't see it hurting anything to mix the two dry and do that as well.
Unless of course your doing more than 50% water changes you should be just fine...
TJ
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75G, 100 lbs LR, Inwatter Stingray LED's, 25 Gallon Sump, 24wt UV, hermits, Snails, pep, fire & cleaner shrimps, Blue Throat Trigger, Perc Clowns , Yellow Tang, Coral Beauty, Blue Regal tang, RBTA, Coral Banded Shrimp, Checkerboard Wrasse, Many Corals, Royal Tux Urchin
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