Using flourescent tubes from an electrical store-you would probably be using "white light". Not particurarly good for plants, but will show up your fishes. Try it and see,if you have problems you can always change to the specialist tubes. Plant food. Well I use Plant Gro, from Nutrafin. It's a liquid plant food and in a well planted tank I feed my plants once a week. There are no phosphates in it so discourages the growth of algae. I would recommend it. Back to your suggestion of making your own fixture. This is a safety warning. You must ensure that the end cap fittings to your tubes and the lighting unit is watertight, otherwise you will be electrocuted. That is why lighting units for aquariums are so designed. They are absolutely watertight where water can affect any electrical live component. Personally I would not recomment a domestic flour.lighting unit for a fish tank. It's notworth the risk.