Yes they should fit as the size is 19/25 of the Proflora so the connector of the proflora has an external diameter of 25mm and the fluval FX6 tubing has an internal diameter of 25mm. However the FX tubing is a bit of a PITA to work with at times with it being ribbed esp when trying to get a seal. Plus the Proflora with an internal diameter of 19mm it will cause a bottleneck and reduce the flow a little, the other smallest diameter fitting on the top of the canister itself on the FX6 which the hose connecters/taps slot on too, which has an internal diameter of just over 21mm