i do occationaly. it is just a fatty acid suppliment. many of the foods we feed out fish are lacking in this. fatty acids help make up proteins. it is a good thing to do but isnt 100% necessary. it is just very benificial and more natural for the fish to have it. Although their overall health would be better and they are more likely to breed with the adition of selecon, but they wont die if they dont have it. iw oudl recomend it.