Sponge filter causing over-active skimmer

[syncro]

My skimmer started overactivating as soon as I added two sponge filters to my sump. The skimmer is producing too many bubbles and is overflowing the collection cup in minutes despite all adjustments. Adding the sponges does not affect the water level around the skimmer.

1. add sponges
2. overactivated skimmer
3. remove sponge
4. skimmer working normally
5. remove lead weight, rinse and re-add sponge to sump
6. overactived skimmer within minutes

These are poret sponge filters meant for fishkeeping: http://shop.riftlakeaquatics.net/LAR...-FLTL001SP.htm

Any ideas?

Thanks,
Brian