Great answer by John!
I grow 100's of bare-root vandas & ascocendas in a Florida greenhouse & recently had to deal with an extreme algae issue caused by an extended period of abject neglect (was traveling since last year) & automated (over)watering. A commercial greenhouse might have answered the problem with 2 gallons of unleaded gas and a match, but I was determined to salvage my plants.
Several different algae, mold, moss & mildew species formed a blanket on the roots. Each layer of algae gave purchase & moisture to the next variety, to the point that even weeds began to take root in the wet layers.
I do not believe that treating first with an algaecide was appropriate. The only thing worse than a thick blanket of live algae is a goopy coating of DEAD rotting algae, which would have created a petri dish for bacteria & other organisms far worse than I already had, sooo ....
Most kinds of algae were removed with a brisk spray nozzle from a few inches away while wet and soft. It came off in chunks and sheets. What a relief to discover fresh vanda root tissue underneath. Even the healthiest roots were not really thriving, though. I took care not to spray off onto other plants, working mostly on a wire screen table.
Cleaned out all dead roots, sterilizing scissors between plants and after dealing with 'mushy' problems.
Used Zerotol (H2O2 solution) to wash everything before and after, soaking the plant.
Treated with Phyton 27 and RD20 over the next couple of weeks to keep bacteria and fungus from attacking tissues damaged by handling. I rarely use such products to avoid phytotoxicity issues, but they can help following transition or shock.
Observation: Areas of intimate root contact + moisture + an assortment of foreign organisms = damaged roots, rot and disease. Some 'combing' and untangling of the roots promoted more air movement between the roots.
I changed the watering schedule to allow a full dry day between thorough watering days and added an extra fan for more air movement. Now I water daily in the hot Florida summers and every 2 or 3 days in the winter. The algae has not returned.
A spash of fertilizer and Superthrive set the stage for a surge of growth, new root tips and blooms ... greenhouse is ready for visitors again!
Just a thought: Your thrice-a-day misting, even in the windy BWI, might actually result in 'farming' algae.