Many fish don't accept new foods right away. All you need to do is get them hungry and keep trying.
Have you used NLS? Have you read the nutrition article on their website or read about the results that so many are getting with it? There is a lot of hype over it but the hype is true. I use it for all my fish and we use it for all the cichlids at work. They do much better on it (color, health, and growth). And usually variety is needed because other foods don't provide a complete diet, which is the goal of variety. That is why variety is preached so much, it was needed to get a complete diet. This food provides it however, meaning you no longer need that variety to provide a complete and balanced diet. I have used many diets and NLS is the best I have ever used (live, frozen, pellets, variety and mixes of the above, etc.).
All I can say is if you have not tried it or have doubts about it (as anyone should with so much hype over one food), take an open mind and read through their site and give it a shot with your fish.