For those of you who build baits for use in seawater. Float testing in tap water is unrealistic, especially if you plan to design close to neutral buoyancy or a slow sinker.
The solution is to make your own seawater equivalent. This is done by dissolving 35gm of table salt per litre of tap water. This will give a specific gravity (sg) of approximately 1.025, the accepted average sg for sea water.
This could be fine tuned with the use of a cheap hydrometer.