increase the available locations for growth the rough granular finish can be provided on the type of plant as shown in fig2 but also on any plant including a typical bushy type plant shown in fig5 and 6 from stem 46 there projects a plurality of branches 48 with many individual leaves 50 each of the stems and leaves provides a rough granular surface finish 52 shown enlarged at fig6 which would include a multitude of protrusions and depressions along its surface to increase the surface area available for the organisms active in biological filtration fig7 shows a typical prior art surface texture provided with stippling the stippling is shown in a grid pattern including vertical grooves 54 and horizontal grooves 56 such stippling still presents large spaces 58 of flat surface areas but does not provide adequate surface area to which the bacteria can adhere this can be contrasted with the surfaces shown in fig3 and 6 in which the surface area is greatly increased the particular rough granular surface area can be provided on the plants in numerous ways one way would be through a sand blasting operation the sand blasting can be achieved either by initially sand blastinq the mold in which the plastic material is.