White tips on SPS

[Albertan22]

Hi all,

I just came home after a month away. My tank seems to have fared well in the care of my tank sitter, and there's nothing much wrong that a water change and some elbow grease won't fix. But my SPS, the only one in the tank (I think it's an acro) has white tips on two of the branches. The coral had lighter coloured tips before I left, but now there's about 2cm of white on two of the branches. The polyps are still extending fully on the white parts, and these branches have also grown significantly since I left on my trip. Anyone know why would these branches would be white tipped? Is it something I should worry about?