// class member
	public Integer givePlayersDaPowaReferenceInt = null;

// in onEnable

if (givePlayersDaPowaReferenceInt == null) {
			givePlayersDaPowaReferenceInt = plugin.getServer().getScheduler().scheduleSyncRepeatingTask(plugin, new Runnable() {
	            public void run() {
	              playersHashSet = FPlayer.getAllOnline();
	              Iterator playersHashSetIterator = playersHashSet.iterator();
	              while(playersHashSetIterator.hasNext()) {
	            	  playersHashSetIterator.next().alterPower(Conf.powerPerMinute);
	              }
	            }
	        }, 120 * 21L, 60 * 21L);

// in onDisable


		if (givePlayersDaPowaReferenceInt != null) {
			plugin.getServer().getScheduler().cancelTask(givePlayersDaPowaReferenceInt);
			givePlayersDaPowaReferenceInt = null;
		}