With CCs measuring at 0.4ppm, you might want to shock up to 10ppm FC in an effort to break them down. Just make sure you lower the pH first to 7.2-7.4 and then run the jets for a bit after adding the dichlor. You want to leave the cover slightky open too while aerating so that CCs can outgas from the tub.
Every 10ppm FC added using dichlor will raise the CYA by 9ppm. So you do want to keep an eye on your CYA while using dichlor to chlorinate.
Got it, thanks so much!