We would like to suggest you install your system with a wrench. When screwing the tank into the adapter (after first attached it to your regulator), the fitting cannot depress the pin to get the CO2 out of the tank. There might be something wrong with the CO2 tank.
It is not compatible with fluval 88g kit since fluval 88g kit is not a US standard regulator and CO2 paintball cylinder.
With this Interstate Pneumatics adapter, you can convert your CO2 pin valve paintball tank to a standard CGA 320 male fitting. Allowing you to attach a CO2 regulator with CGA 320 thread to a paintball CO2 cylinder.