they don't eat liquid food. that is a long tentacle plate. they don't have a very good track record in closed systems. in other words, don't get attached to it.
if you wanted to feed it, a small piece of meaty foods is what they like. a pea sized piece of fresh fish or shrimp will work.
if it's not getting enough light, you should purchase a better light, instead of balancing it on that skull.