Just stumbled across your post… don’t think you’ve visited our thread yet, have you?
Further, it’s not just that the commercial aquarium controllers are pricey, the core functionality is pretty limiting relative to what can be achieved with HA. For instance, APEX controller breakout boxes cost about 200 bucks & contain nothing but an SPI bridge. Don’t even get me started on High Availability functionality… APEX doesn’t offer it.
As a cybersecurity professional with 15+ years working for GSM network operators, I used that experience to build something a whole lot better than an APEX, Tunze, and various other aquarium controllers.
And yeah, after 2 years of research and testing with my 12 marine / reef aquariums, we’re readying an initial product for commercial launch this year, with several ‘accessories’ lined up to follow. 
https://community.home-assistant.io/t/going-to-next-level-of-aquarium-automation-whos-with-me/