How can I break up my coconut fibre plantation soil brick (before soaking)?

well 5 gallons is too small for hermit crabs ... and one of those bricks would be too much but you can prepare all and then what you don't use lay it out to dry ... i have done that before ... unless you know someone really strong or with a saw to cut it, i would just prepare the whole brick ... but you should consider a 10 gallon and keep the 5 gallon for the molters/isolation ... once you have everything you need in the 5 gallon the hermit crabs will not have any room to walk around ... i know, i started with a 5 gallon :O)