I had a 29 bio cube as well with all the extras. it was very successful, I finally went to a 150. anyway, I had the same issue, and changed the thing over and over, even the whole unit. The thing probably doesn't do anything. really, it's so small and undersized, almost all cheap UV's are undersized and just there to make you feel better. the bulbs have to be big, lots of wattage, and flow has to be very slow for it to be effective. check out Emperor Aquatics, and read up on their UV's. just for the knowledge, they get one that's actually big enough.