I am not familiar with the Fluval 1000. Is it a system, or a filter of some sort? Any how at 42.3 gallons, this tank can hold a pretty good amount of fish. Well...you want two Clownfish. Depending on the species, I believe you could keep about six other small fish. If this is your first marine set-up I would stick with gobies, damsels, cardinalfish, bassalets, dottybacks, hawkfish. These fish are on the easier side to care for. In contrst do not buy butterflies, Angels, Tangs, Triggerfish, and Seahorses. They get much to big for a 43 gallon tank and some require a ton of care. You didn't mention it, but a good protein skimmer and some live rock would really come in handy.
Good Luck, Sam Reef
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90 Gallon FOWLR Marine System
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