Can’t get rid of smell…?

Creepy_Steve is correct - you have reached the capacity of your carbon filter at that fan speed. You can place an additional carbon filter inside the room with a fan on top and NO DUCTING. This will clean the odor before the other carbon filter extracts it. I find it better to have a spare carbon filter and spare fan of the same size on hand rather than buying a bigger, more expensive carbon filter and the bigger fan along with that. I used this setup to keep the bathroom actively stink free when I was showing my house to buyers.

Probably need a more powerful extractor fan. That ducting is quite long for a 5 Inch . Shorten the ducting or get a more powerful extractor fan. Also how old is the carbon filter ? May need changing.

I found that having my filter outside of the tent worked best for me. Although I only have a small tent for 2 or 3 plants.

You need a in-line filter I lice in an apt and have a 4×4 grow tent with a 4 inch fan with a in-line filter and I vent into the apt with no smell at all with up to 6 plants

if you have negative pressure (tent walls bow in slightly), it's the carbon filter that is the problem. it's not doing it's job one way or another. some brands are better than others. if you can get details on the amount of activated carbon (in grams usually) you can better compare products. if they won't divulge that info, i'd avoid it. also, ensure the CFM the filter is rated for is not exceeded. not all duct fans are the same. The static pressure it can operate under and still move enough air is equally important to "cfm", if not more important. easy to tell.. is air moving out of the duct at a decent rate and creating negative air pressure in tent? if so, it's fine and the smell cannot escape except if carbon filter is not good enough.

Shorten the length of the ducting, that length of ducting will be screwing the efficiency of the extractor fan and by side effect the filter.