Probably diatoms (brown algae)... Its much easier for brown algae to go away after cycling is over because even though the light will still be there, the trace ammonia that triggers the diatom spores will be less in evidence.
There are several things in my mind (and I consider myself to be still learning this) that can serve to have an impact on algaes like brown algae.
1. Good filter flow (amount of turnover in the tank) will give the bacteria more attempts at processing the ammonia because it will be pulled past them more times per hour.
2. Good tank circulation (many larger tanks use extra powerheads to assist in water circulation out in the tank) will reduce the number of "dead pockets" where water doesn't move and ammonia can hide (a good example of these is usually in the corners between substrate and tank glass - if you see brown algae there you are getting to see an example of a dead pocket!
3. Healthy plant growth (actual increase in plant size, not plants just being there) can help in the sense that plants will use some of the ammonia in the tank. A large volume of plant mass can have quite an impact.
4. Light balance (the balance between too little for plant needs versus excess being available such that algae stimulated) is of course the major player. Figuring out the minimum brightness and time periods for healthy plant growth is the number one tool in algae avoidance I believe (at least at my particular stage of learning
)
Note that all of these are just subheadings under the basic truism that "Light + Ammonia = Algae" that our planted experts like to remind us of when the periodic newcomers come along and insert the old myths about algae ("to much Phosphorus" (this is not true, P is a needed plant nutrient and does not stimulate algae when used properly) and other myths..)
~~waterdrop~~