Some nice designs there , I like.
I was going down that path until i ran into a pool sand-filter on ebay ,, 220 litres and brand new , paid $40. Of cause i will fill it with bio-balls and pot scrubbers NOT sand.
Nice to have the valve? unit on top for flushing etc ,, but basically your wheelie bin do's the same job AND recycles an unused item ,, love it.

You did it to yourself , the Karma .
You did NOT steal the bin ,, you decided to assist your former neighbours in disposal of an unused item that was potentially an environmental pollutant:)
New I should have been a Lawyer

Great use of a wheelie bin. I turned one into a fish tank for my first system.
Have you thought of a duckweed tank to take some ammonia and nitrate out of your system. Makes good fish food.

On the filter if you had a sealed chamber at the top before the water went down to the base you could place your mechanical filteration at the top where it could be cleaned easier.

I wonder if some one who knows might post some conversion info for us. The conversion info I'm speaking of would be the volume of bio-balls compared to a volume of gravel or clay balls.

As in how much flood and drain grow bed can a particular amount of such a bio-filter compare to? I know there are media out there for bio-filters that can support a huge amount of bio-filtration but they seem to require pre filtering solids out before they get into the bio-filter and they also seem to require a huge amount of air bubbling through them.

If I move the larger aquarium back indoors, I don't have the flood and drain grow beds to handle too much stocking in there (only 5, 5 gallon buckets which is only a little more than enough gravel for the small aquarium.)

nice work Bentaz, those explanations are spot on. Good picks too.