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There are definitely no eels in the hobby that could be kept responsibly in a 24 gallon tank, but there are a few, small predators that could work:
-Wartskin Anglerfish/Frogfish (anglers are notoriously difficult to keep long term - I have a bunch of info on their care you can read through if you want to try and keep them)
-Coral Crouchers (these are scorpionfish, so they're venomous; handle with care)
Alternatively, you could do something like a small mantis shrimp (Stomatopod) species - those can be really cool.