well unless you have already identified the problem, i think the problem with the large changes, given that the new water is good and temperature matched as well, is that something will be changed drastically... and not necessarily something you can/do test for. there's so many things that might be off taht we just cant account for... we dont even know the complete chemical composition of real seawater. while a large change can be good, it's not something to be done blindly or regularly imo. if you do know what the problem is, then yes, act accordingly.
yes i agree that a large change can solve quite a few problems, but most times, the aquarist doesnt know what the problem is (which is my point), and there are inherrent risks in a large change itself. i suppose it's a balance thing. does the risk outweight the benefit, or vice versa? i dont think we can generalize that.
Q, yes, a single area of a few gallons in the ocean does get a 100% change many times a day, but that is not a rational comparison due to scale. it's like taking a look at one cubic centimeter of our tank and saying, that it gets 100% water change numerous times a day within our tank. but a change with what? the same water that was previously occupying it. so really, nothing changes. i suppose you could say the ocean is a small tank with a near infinitely large sump... which obviously cant compare to a closed system tank.
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