power filters like you stated are HOBS
simpte is right - just like to add, the HOT magnum 250 is a "hang on tank" canister filter made by marineland. there's an option to run a bio wheel 30 with a T connector on the outflow. I've had a couple of these, and I liked them when i used them in the past. Marineland has the 220 and 350 canisters, and there's a optional hanger to "hang on tank".
What's really cool about the magnums, is the optional micron cartridge, easily converting the filter to a "diatom" filter. diatomatious earth powder is either hated or liked, recommended or not recommended. Primarily used for "polishing" established tanks.
edit: i'm currently using Hagen Fluval 404's (2 of them on my 125). Only because i could get two of these for the price of 1 Eheim canister.
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