I have a 5g tank that has a 9w fluorescent bulb in the hood, and I've had the light running since january of this year. The only plant I had in there was java moss, which was growing pretty nicely until about a month or so ago. The moss started becoming squiggly and thin, as opposed to thick with nice fronds which is what it started out as. I haven't changed anything in the tank such as water parameters, etc. and I do weekly wc's of 50% or more. Does my lightbulb need changing already or could the weak growth be happening because of something else?