Equipment questions come from beginners and from people twenty years in, so say roughly where you are and what you are trying to achieve. For a buying or sizing question: Tank size and what lives in it. A filter that suits a planted shrimp tank is wrong for messy cichlids of the same volume. What you already have , and why it is not enough — flow, noise, capacity, reliability. What is available to you locally , which decides far more than the theoretical best product. For something that has failed, say what it is doing rather than what you think is wrong: "the heater will not switch off" and "the heater is broken" lead to different replies. For DIY builds, photos and measurements, please — a build thread nobody can copy is just a picture. Anything involving mains electricity near water, say so plainly so people can answer with that in mind. One house rule, and it is the only one that matters: answer the question that was asked, and say when you are not sure. A confident wrong answer costs somebody a fish.