Hi,
I’d like to add that I’ve had the same issue. I’ve had my Reef Factory Dosing Pump Pro X4 for under one year and one of the heads made an awful noise one day and found it had broken into pieces similar to yours. I searched online for a new head and couldn’t find one. I sent a message to Reef Factory and a little back and forth and he said they are hard to get and not even available in the USA. He shipped me a new head from Poland which was great and told me that BRS placed an order for some to arrive in April 2025. A more recent online search shows them available in Europe but with three options and they all look the same, but are not.
Head L = large dosing pump CR/ ATO
Head M = dosing pump pro
Head S = no idea what this is for…. Smart tester?
I received head M and it fit my dosing pump perfectly. I just hope these heads are affordable because they seem to break quite easily. I already hear another head about to break. Overall I love the look of this doser and how slow it dispenses, but if the heads are expensive, I may go back to their regular doser that has replacement heads that are only $20.