What Should The Specific Gravity Be In My Aquarium?
February 27th, 2012 Tags: 
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Although there are currently a few saltwater fish hatcheries, most saltwater fish sold in fish stores are collected from the oceans. The salt content or specific gravity of ocean water varies in different parts of the world as well as individual oceans. These saltwater fish which are collected from various oceans are shipped to aquarium stores and homes and are expected to live in whatever specific gravity the aquarium keeper decides on.
Back in the 1980’s and early 90’s I recommended my customers to keep specific gravity for their saltwater fish aquariums at 1.020. The theory back then was that parasites were less prevalent at lower levels of salt. This theory has been proven completely wrong – parasites continue to thrive at this level. Specific gravity has to be much, much lower to kill parasites. The flip side is that most fish also thrived at a specific gravity of 1.020. But then I recommended my customers to keep specific gravity higher in aquariums with invertebrates and live corals.
Eventually it seemed to make sense to maintain a common specific gravity for all the saltwater aquariums in my retail store and in my service aquariums and we began keeping all of them at 1.023.
What I learned from my customers and my service clients over the past 25 years is that fish and corals can live and thrive in a wide range of specific gravities and many of these fish and corals have lived for over 15 years. The key is this: keep stress low by keeping as many parameters constant as possible. In other words, choose a specific gravity between 1.020 and 1.025 and then keep it constant! Currently I recommend keeping specific gravity at levels between 1.023 and 1.025. To keep other parameters constant I recommend using timers on lights, keeping water quality optimum through regular water changes, feeding at the same time(s) daily, adjusting the temperature and keeping it stable.
So if you want to have beautiful fish and corals, and want to keep your aquarium at its healthiest, salinity, temperature and other parameters must be consistent!