This look like a blue haliclona sponge, so it's photosynthetic and does not need other type of food.
I put some zeovit sponge power in my tank, 2 drops per 70 gallons and that's more than enough. If your coral are not reacting right with this product, you should not use it. In any case, you should always start very slowly with any food additive.
The only thing that might kill such sponge is exposing it to air. It's pretty tough. I have mine for a year and half and a few pieces broke and I put it on my live rock and in a day it was attached. You did well to take a large colony because they grow very slowly. Sponges can live very long and some are thought to be immortal
