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I would put the ceramic beads in the AquaClear, then the old established Marineland media, then the AquaClear sponge on top. If that doesn't fit, then use the AquaClear sponge and the Marineland filter media.
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Uhm....no. The sponge (or more than one) always goes in first to trap detritus as the water travels bottom-->up through the media. You want to keep any bio-media as clean as possible. So you have sponge(s), fine filter pad, then any chemical media (I don't use any), then old, followed by new bio-media last.
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I fill my Aquaclear's completely with sponge material as I have found that bio-sponge is every bit as good, or better, than ceramic or rock like medias. So I use two standard Aquaclear sponges, then a pad, and fill the rest with finer, custom cut bio-sponge. So I basically have HOB sponge filters. I will also use a pre-filter sponge on the inlet tubes, increasing bio surface area further and as a food and fry saver. (I feed flake food and rather than have some get sucked into the filter, it sticks to the pre-filter sponge and fish will later pick/pluck it off.)
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Alternatively, I often start new tanks by rinsing/cleaning sponge from an established tank in the new tank water. Although debated on this forum, I've found over the years that enough BB is transferred to seed the new filter.
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I do agree that the AC50 is better than the AC30 for the increased media space. (My two AC70's on my 60g use AC50 impellers for increased media space and reduced flow rates - both set for minimum flow/max re-filtration).