AquaClear 500s are the biggest the company makes. They turn over a lot of water. Don't know anything about Renas but have had lots of experience with three AC 500s on a 180g housing oscars, also very messy fish.
Filter media NEEDS to be cleaned weekly and bottoms need to be siphoned weekly to keep nitrate levels low. AC 500s are easy to get at the filter media compared to canisters, imo. Never owned a canister because they all looked so dang hard to get opened and closed, then primed again for use. I'd say go with the AC 500s. They're efficient and easy to use.
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