Sorry to hear about your star. How long did you acclimatise it for ? Starfish are prone to osmotic shock whereby they litterally disolve from the inside out, unless you give them several hours getting used to the new conditions, unfortunately this procedure must be carried out all the way along the chain else the even if you do it right the damage may already have been done.
Think you may need to be a bit more specific about exactly what coral it is. There's so many generic names that people use that can be several different sp. it's best to use the latin name so there can be no confusion where possible.
The only coral I've heard called watermelon is a mushroom.
In a nutshell you want good quality, well cured rock but have to remember that if it's out of the water overnight in the cold, like it is now, then there will be some die off even though the rock was previously well cured. In an empty tank that's no problem but in a stocked tank then the spikes in ammonia, nitrite etc could have disastrous results for your live stock.