Is it sitting flat on the bottom?
If so that will block any water intake through holes in the bottom anyway. You can put them there if you want. If you want it to be able to draw water in from the bottom, raise it up a little by putting something under it. Maybe attach 4 knobs to the bottom like feet.
That will utilize more of the filter surface inside the tub. But it will also cut down on the suction that you did have. The more holes, the less suction.
