No negative effects at all, quality frozen food is pathogen -free and fish generally accept it readily. Consider that feeding a single frozen item is generally not sufficient for complete nutrition. You should offer an array of frozen foods, supplemented with pellets. Brine shrimp is not a very nutritious food, if you must feed brine, try spirulina brine, its a little more nutritious. With so many frozen options, you should put several different items into your feeding rotation.