Please can someone help me with what this issue is. Im thinking calcium. Im in week 3 of flowering. The tips are starting to yellow.

For sure. Take a look through Mr. Growits articles under plant problems. A lot of great info there. Also, take a look at the Read Me at the top of the forum in case you have any other questions or concerns. The more info the better :)

Thank you. Ill give them a flush and see were that leads.

No need for a flush just yet. Monitor and maybe do a PH water only feed next time and dial back the nutes a little.