ive bought a big acrylic fishtank to settle my bio in will bio attack acrylic

I don't think it will last very long. It looks like the methanol will attack it over time.
Chemical resistance in general use for clear acrylic plastic

Ken

its to settle bio after the process so meth will evaporated its just to settle off before use

Freshly reacted biodiesel has methanol mixed in it. Are you doing something to remove the methanol from the biodiesel before putting it in the settling tank?

Ken