You're right, you don't want to overdo it. Alot of people do. It's easier to add more fert than to wash out too much once it's in your soil. As to how often to fert, it's up to you. I don't recommend that you use the fert with every watering. And don't water too much as you should let the soil dry out some. Roots need oxygen and the only way they get is by allowing the air to get into the soil, and the only way that happens is to let soil dry out some. Water in soil can't coexist with air as water always pushes air out of the soil. What plants have become used to is a wet-dry cycle which is the way nature handles things. What you're really trying to do with an indoor grow is create conditions that are like that of nature. dynagrow is a synthetic, fast-acting fert and not much is needed to make a big difference in your grow. There are a ton of ferts in the local grow shop but you only really need one provided it has all the nutes plants need to grow. dynagrow actually has two ferts - one for grow or veg, and the other for flowering. When it comes time to flower, it might be worth spending the money on the flowering fert. Just be carefull how much you use of it. Just give water in the last two weeks of life.