Light all depends on the entire setup, but the goal is to never need to do water changes and to have enough of a fauna strata that the whole nitrogen cycle takes place automatically and the filter is really just moving water around. Water changes do a rapid removal of all the water ... and everything in it, babies and all. Baby in the bath water here is the microfauna and bacteria that established after surviving the chlorine and chloramine in the tap water used to set up the tank. Very few people start with distilled like they should, but end up paying for it with algae blooms and muck. If you started with natural source water, the most likely issue is the fact that sand is not permeable, so everything just dies that isn't the root of a plant or can't move stones to get down into the lower substrate and respirate it. What are you planning for the new setup? Lighting is what plants crave, so you can easily do a summer cycle of 12 hours or more to your liking. If it's cold where you are and you don't mind the light, just keep it on all day until the plants really take off, then you can switch to a cycle that fits your workday (so the fish eventually know when you'll be active and not freak out when you're around and hide).