First potential trouble area - gravel substrate. While it is quite common to use, the relatively large areas between gravel particles permit uneaten food and fish waste to get down into these crevices where the decompose thereby fertilizing algae. Although I personally prefer sand foe this reason, gravel can be successfully kept if vacuumed thoroughly weekly.
Secondly - It sounds like you have been feeding too much, thereby enabling the above issues. Try feeding a lot less at each feeding but feeding a few times daily. Just what the fish actually eat leaving none to scavenge for. Any herbivores should receive supplemental feedings instead of being asked to make up for poor husbandry.
Third - The beneficial bacteria that comprise the biofilter exist principally in the filter although they do live on every surface of the tank. Vacuuming the gravel substrate will not remove enough of them to matter. Those lost will be replaced in a short time.
Fourth - If you have no live plants, the fish will be happy with ambient room light most of the time. Your aquarium lights can be placed on a timer so they come on and off at the same time each day. You can set those time for your convenience. Remember, the first thing to consider is consistency. Fish learn to work around the timer even though they cannot read.The predictability will enable them to avoid the panic times that happen with irregular lighting cycles. You can shorten your lighting cycle if you have no live plants thereby providing less energy for algae/diatoms.
Fifth - Your test kits are probably innacurate. Please check the expiration dates.
Charlie
