The influence of photoperiod on biological cycles in an aquarium was investigated in this paper. The research was divided into three cycles with different duration of the photoperiod - the cycle with 12 hours of light (F12), the cycle with 8 hours of light (F8) and the cycle with 16 hours of light (F16). Changes in abiotic factors - temperature, pH, concentration and oxygen saturation, and nutrient concentrations - total ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and phosphate were monitored. In addition, the concentration of chlorophyll a was monitored. A statistically significant difference between samples from different cycles was observed in the values of temperature, pH, and dissolved oxygen. The highest recorded values of temperature and dissolved oxygen were in cycle F16. The pH value was the highest in cycle F12, as was the concentration of chlorophyll a. Given that there was no significant difference in nutrient concentration between cycles, it can be concluded that photoperiod has an effect only on the amount of oxygen in the aquarium, and therefore, in order to save energy photoperiod of 8 hours of light is sufficient.