Gary - I would suppose it would depend on how the bioload in your fuge compares to that of in your tank. Atleast as far as the level of photosynthetic organisims.

I'm not an expert by any means, but logic would tell me that if you leave the lights on all the time over the fuge, then that level would stay the same and when the lights over the tank turned off, you would still have a noticeable drop in your PH there. In that situation there is nothing to pick up the balance that was being used up by the main tank. When you have your lights running in a reverse cycle, your fuge will pick up where your main tank left off. This assumes you have a decent amout of life in your fuge. Again, this is just me using my logic and of course Spock was wrong at times, lol