On the lighting on my fish tanks I use fluorescent tubing of different length. Each tube has a power unit and starter. These units can be bought in different watt outputs. More or less its made out that if you have a small fluorescent tube with a small watt usage, you get the respective power unit. E.g. if you have a 15 tube you get a 15-18watt power supply unit, if you have a 40 watt tube you get a 40 watt power supply unit. In sure a mate told me that buying a unit of a higher watt unit than the lamp required eg a 40w unit supplying power to a 25w tube would not affect the tube and would be safe, as the 40 watt was the max power of the unit and the tube was the one drawing the power, whereas if I bought a unit that say supplied 25w and then used a tube 40w it would burn the unit out. Is this true?