"Does Seasol make grapes taste salty?"
Seasol, and other commercially available kelp based products, are harvested from the ocean. The kelp is then prepared into a solution either by physical and heat extraction, cold pressing (like olive oil) or by using enzymes to break the kelp down.
Seasol is 0.33% w/v Sodium and 0.92% w/v Chloride. In rough chemistry this means in a litre of Seasol contains 0.33 grams of Sodium and 0.92 grams of Chloride.
If you applied three applications of Seasol in a season at 5 litres per hectare, 15 litres in total, you would apply approximately 5 grams of Sodium and 14 grams of Chloride. This is a small amount in comparison to amount per hectare to that salts deposited in the soil from common practices like applying super-phosphate, gypsum and of course irrigation water.
Irrigation water at 800ppm of salt (800 mg/l) applied at 1 megalitre (1 million litres) leaves 800 kilograms of salts (0.08g x 1,000,000) in the soil.
The amount of salt applied by the Seasol is negligible compared to that applied as irrigation.