Trickle Filters

I was visiting a large pet centre in Montreal (Quebec , Canada) and
noticed that their tanks had an unusual filtration system: they did not
have individual pipes to pick up the water from each tank; instead the
tanks had skimmers and the water dropped behind the tanks into some
reservoir below the tanks. The return was a continuous flow pipe from
tank to tank to tank.

I was always under the impression that Trickle (Wet/Dry) Filters were
used for Marine Aquariums; Can they also be used in Freshwater tanks
too?

Is there a good website that has DIY plans for a Wet/Dry for a
freshwater tank?

Thanks,

RobGN.

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