How to get lionfish to eat frozen food?

Thanks for all the grate advice I have had on here but yet again in need of more advice. I have a lionfish and have had him around 3 months now. I got him when he was very small and is still quite small. I always feed him live brine shrimp but have tried to feed him frozen food and he is not interested. First I tried frozen chopped mussels to try and change his diet a bit but he did not eat it then the shop where I get then from didn't get a delivery because of ice on the road so I got some frozen krill what look very similar to them and he had not eaten for 4 to 5 days and I had been advised to wait around that long anyway before changing his food because it will make him more likely to eat something new. It would be good to get him to eat new things to change his diet and incase they miss a delivery again. I have a brittle star that went crazy for them do why won't the lionfish eat it? I have a 200 litre tank.