If you want to connect 9 Fans, it is recommended to use the Splitty9 Active. The Problem is the Aquaero, not the Splitty9.
Each Fan connector on the Aquaero 6 is rated for 2.5A. (Read the manual, Page 8 on the PDF:
https://aquacomputer.de/handbuecher.html…o_6_english.pdf
aquaero 6:Maximum current is 2.5 A per output independent of output voltage. Outputs will be switched off if amplifier temperatures reach a critical level and will automatically be reactivated when cooled down.
If an output current of 3 A is exceeded, the output will be permanently disabled. To reactivate the output, the aquaero (or the complete PC) has to be disconnected from power for a short period of time.
Your Fans need 0.3A each, so you can only connect 8 Fans to a Splitty9... Overcurrent protection will prevent damage on the Aquaero, but the Fans will stop spinning...
A Quadro or Octo are rated for 2.0A on each Fan Connector.
I suggest you buy a Quadro and connect it to the Aquaero6 with an Aquabus cable. This gives you additional 4 Fan ports that are controlled by the Aquaero.
Then buy 5 regular Splitty9. Connect 4 Splitty9 with 6 fans each on the Aquaero, 1 Splitty9 with 4 Fans on the Quadro, and the two Pumps on the Quadro.