I've used Selco in freshwater, mostly as an adjunct for gel diets or tube-feeding fish that aren't eating. Selcon is a bit problematic for me: I buy Selcon or related HUFA mixtures that must be refrigerated after opening, and have a short shelf-life. I've never been able to reconcile the idea that Selcon (the name implies it is related or derived from Selco) doesn't require refrigeration.
Jay