It has been a long time since i used T4 fixer as i hate to pay shipping on water. When i did, i didn't use HCA as I follwed the Formulary recommendations; and i was using their product.
Now i use Ilford's Rapid fixer and I do use HCA before and after toning. I believe Ilford has standize the name to hypan but it is the same stuff.

Don't know if this helps you are not. When I used T4 i did run some hypo check test and it tested just fine and i did follow the directions provided by PF which was not to use HCA.