Hi,
Pearling shouldn't even be on your priority list right now. You have basic plant husbandry issues that completely override the issue of pearling.
Problem number 1 is that you undoubtedly have too much light which fosters the rise of algae. You need to completely shut down 50% of your light to give yourself more room to breathe.
The dark beard-like algae is BBA and this results from a poor combination of high light and poor CO2. Increasing the dosage and lowering the light therefore affods the best chance of eliminating this species.
Increasing the water change interval is one of the worst things you could possibly do to combat algae. You need to reduce the interval, probably to 2X or 3X per week. Once under control you should never go more than a week without a water change.
Cheers,