An old thread I know but just wanted to add I've kept FWT fish since I was 14 that was almost 50 yers ago..... I broke from them 15 yrs ago and went marine until the house got flooded in 2018 and crashed the setup. By then I'd got my brother into marine and when he up graded 3 years ago he gave me his 90 ltr Aqua one set to start again.
I didn't, I went FWT again. I've now had the system running for 3 years with no mechanical filtration. I've lava rock in the 1st sump compartment with the heater and Pothus in the 2nd with the return pump (wrapped in fine gauze to stop roots clogging the impeller) The gauze still allows the odd daphnia to slip through which the fish love.
Since then I have never vacuumed the substrate, I don't clean the glass (scrapes on the glass are from when my brother had it) and do a 50% water change every other month or so. I used to run a cannister filter but never had the setup in as good a state as when running the sump. I highly reccommend using one if possible.
