Yellow Water

From the fact that you are attempting a fishless-cycle and would appear to have live plants, I would assume that two things are true

• You have the lights switched on for at least part of the day, otherwise your plants will not survive.
• You have non-zero ammonia levels To drive the cycle, this is required.

Our great-Cycle expert on this site came up with a saying "Lights + Ammonia = Algae". The primitive forms of algae have developed to use ammonia as an efficient source of nutrients. Algae is a common problem within the fishless-cycle and beyond.

There is a web-site that can help with the different sorts of algae that may be present. For "Green-Water" algae, the primary cause is given as "High Ammonia". Given your circumstances, the only control solution you have is to reduce the amount of time that your lights are switched on using a timer-switch. 7-8 hours a day should be plenty for real-plants.