i keep hearing this popping or cracking sound coming from my 150g tank.i read on the forum that pistol shrimp make this noise,but i didn't put a shrimp in and i never seen one in their.
try to locate where the sound is coming from and when the lights are off, use a flashlight to search. if you see a pair of glowing eyes looking back at you, it's a mantis. also mantis move much faster than a pistol shrimp. try putting a thawed silverside near his lair if it charges out quickly then it's most likely a mantis.
If it is a mantis shrimp your tank is safe.
I have heard of them cracking small glass tanks. You are fine with acrylic and I dont think it would crack a large tank unless it was so big Mr Magoo would see it.