[jon.smolders]

Could it be the confusion with hydrometers that were not calibrated to the proper temperature?

Martin Moe in the Marine Aquarium Handbook says that a hydrometer calibrated to 59 degrees will give a reading of 1.022 at 80 degrees, when the true reading should be 1.026.
John Tullock in Natural Reef Aquariums says in a chart one part of his book that the recommended level is 1.022-1.024 (page 119). In another part he explains a bit further, saying that "A typical glass hydrometer reading should be 1.022-1.024 at 75 degrees F" (page 67) but then tries to explain how temperature affects reading. He also says that seawater is 35ppt which "corresponds to an observed hydrometer reading of 1.024 at a tempurature of 75 degrees" (page 121) - No mention of whether or not that hydrometer is calibrated to 59 degrees or 75 degrees.

Confusing.

Anyway, tullock also says "Marine Aquariums are often maintained at a lower specific gravity in the belief that the lowered salinity reduces stress on fishes and makes the survival of parasites less likely. I am aware of no evidence to support this practice" (page 121)

I seem to recall the reason being that the lower salinity made it easier on the fish because they didn't have to work as hard to offset the loss of water from their bodies because of osmosis.

I keep mine at 1.024 at a water temerature of 78, read with a hydrometer calibrated to 75 - whatever that means.