Now this is something that is quite important. Every grower needs to determine the right size of their pump. The size of the pump depends directly on the size of the reservoir that you have. The larger your nutrient reservoir, the larger your air pump has to be. However, calculating the exact size can be a tedious process. This is why most growers actually go by the unwritten-rule of choosing an air pump - they go for something that can provide their reservoir with about 500-600cc of air per minute. (For those new to growing, this is the same as about 500-600ml of water per min). This will suit the needs of most indoor growers. However, in case you are a commercial-scale grower, you might be looking forward to something larger and more powerful.