I've got myself an Arcadia twin (2 x 54W) T5 starter unit off ebay, but there's no instructions (unsurprising). Do I have to put both tubes in for it to work or will it work with just one tube? Also, it's 54W - does this mean I have to use 54W tubes or can I use lower wattage tubes with it? Can I mix tubes. i.e. one 2' tube and one 3' tube or do they have to be the same?