safe support material for AP

[Brent Wheeler]

hi,

Due to space requirements I have my bio filter suspended on a grate system (kind sold at outdoor coy pond stores)  in my sump tank.  however it is not able to hold the weight on just the leg holes, it breaks though after several months of use.   

What sort of material or blocks can i use in the sump tank that will not leach into the system. to support this grate.