Is 15W enough for the plants? I've been aiming that bulb for my Archae 27W replacement bulb.
the bulb I'm using is 18w and for a 5.5gallon I think it's just right. my plants seem to be responding positively. And if you are a believe in wpg rule of thumb, that's about 3.27wpg compared to the former which was 4.9wpg. I think the reduction in intensity also provides a little more room for error. We shall see.