This section is for the first few months, when everything is new and half the advice online contradicts the other half. There is no question here too basic — the people answering all started where you are, and most of us killed fish learning what you are about to ask. Tell us four things and the answer you get will fit your tank instead of a generic one: Tank size in litres or gallons , and how long it has been running. Almost every answer changes with these two. What is in it — fish, plants, and whether anything is already unwell. Your filter and heater , by name if you know it. "The one it came with" is a fine answer. Whether you have a test kit , and the readings if you do. If you do not, say so — it changes what we can work out. If you have not bought anything yet, that is the best possible time to ask. A tank that is the wrong size or in the wrong place is much harder to fix later than it is to get right now. 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.