they only flare/flourish when they are fed. If they boom, then there is a problem in the tank with weak water changes, poor skimming, weak water flow, etc (accumulated nutrients). Until that is taken care of... any fix will be temporary (they will return with a vengeance).
many folks have a few majanos in their tank and a year later... still only have a few. Its a sign of good nutrient control.
Use this as a beacon my friend. Manually extract what you can (swap rocks... chisel them off clean on other rocks you want/need to keep)... but above all, reduce nutrients. Is your water flow at least 30-60X turnover per hour? DO you thaw your frozen food and decant the juice away before feeding it? 25% monthly water changes bare minimum (10-20% weekly even better)? Is your skimmer tuned to produce a full dark cup of skimmate near daily>
If answers to the above are no... then its doesn't take too many months for nuisance algae or nuisance anemones to flare up.