Nope other than the two main holes for placing the decor, my tank has one tiny circular hole that could fit only a cord for a heater, and a bigger slot for the HOB filter or intake and outtake tubes for a canister.
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That sucks man. You can keep that 204, add the Ac 50, remove the carbon and replace with another foam insert and maybe add spongefilter/powerhead combo and bam you have double the filtration as you had before. Or if you could buy a bigger canister you and move your old 204 bio media into it. You can find good deals on Craigslist or at used aquarium stores. There's this used aquarium store here we got a like new API canister rated for 175 gallons at a fraction of the price ($60). The deals are out there, you just have to dig a little.
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