If your water is very low in nutrents (NO3
) the cheato will not grow..
The normal light cycle is 12-24 hours on a fuge though (normaly reverse photo-period if
less then 24 hours)
and a daylight spectrium bulb like the one you have is best.. 5000-6700K or so..
My guess is the light isnt on long enough.. your bulb isnt intence enough for the size of
your fuge.. or you dont have enough nutrents for the cheato to grow.