the biggest tank i would use a penguin 350 on by itself would be a 30 gallon. is the water flowing over the cartridges in the penguin, because there shouldnt be any visible debris getting through the filter. the black foam on a whisper filter is just there for biological filtration after you change the biobag (the white cartridge). so the black foam shouldnt be adding any mechanical filtration and should be in front of the white cartridge so the water goes through it after its already gone through the biobag. there is no doubt that you need more filtration. and on a well stocked 75 mbuna, A LOT more filtration. definitely a fluval 405 at the least. the fluval 405 has a big course mechanical cartridge, then the water goes through 4 stacking trays from bottom to top. for the bottom 2 trays i would cram as much filter floss in them as you can get. after the first one or two cleanings the water will have compacted the floss even more so you should add more. the third from bottom tray (second from the top) should be filled with a carbon that wont get through the slots for the water. the first time you can use the carbon they give you, but you should change the carbon everytime you clean the filter. the top tray should be biological. they give you 4 pouches of a porous ceramic biological media, just fill the top tray with it, you will have a little extra that i just didnt even use. whenever you clean the filter just check the biological and dont mess with it unless there is debris in there, in which case you should simply rinse it off with tank water. any time you clean the filter rinse the course mechanical and filter floss until it is clean. eventually you will need to simply replace the floss.