I have a Marineland Emperor 280 and 400 and both have 2 slots for additional trays, with the exception of the 400 having another 2 slots on the other side. So I would have to assume that the Emperor Penguin 150 has 2 slots for media trays also.
Your filter should have a empty media tray and a media pad with carbon. The media pad is used for mechanical and chemical filtration, while the media tray can be used for additional chemical or biological, by adding the proper chemical or biological media in there. You have the option of filling both slots with a media pad and media tray OR 2 media pads (if you purchase an additional pad) OR both media trays (if you purchase an additional tray).
I used to use the media pad in the outer slot and fill the media tray with carbon and zeolite. I later learned that carbon/zeolite is not necessary to use as it was getting expensive to replacing the pads. So I later just rinse them often. Eventually, I just used the one media pad for mechanical filtration.
So in answer to your question, you should at least use the media pad and it is your option to fill the media tray with some kind of biological media.
It won't hurt. The more media the more room for bacteria to grow, the more carbon to help clean the water. Part of the reason for the extra slot will depend on how old the filter is. This is a company that makes regular changes to their filters every few years in an attempt to improve them and keep up with the newer competition on the market.
Something that works good in that extra spot is a sponge. Many of the sponge inserts they make for the Whisper filters by tetra will fit into the Penguin filters. This is cheaper for the consumer, collects bacteria without needing to be changed monthly, so preserves the culture better, and when it gets dirty, simply wash it in dirty tank water during a water change, and put it back in. Just be sure not to rinse filter media under tap water and then put it back in. The chlorine in tap water will kill the bacteria culture, which makes the use of a sponge pointless.
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