How to fix alert on every tick?

Hi Guys!

I have an ADX-cross indicator. I added alert, when DI+ and DI- crossed each other, but the alert comes on every tick, which is very annoying.

I just inserted 2 rows: Alert ("Cross UP") and Alert ("Cross DOWN") - else everything is left original.

 How could I fix this problem? Thank you for your help in advance!!!

 Have a nice day! 

Here is the code too:

//+------------------------------------------------------------------+
//|                                                   ADXcrosses.mq4 |
//|                      Copyright © 2004, MetaQuotes Software Corp. |
//|                                        http://www.metaquotes.net |
//+------------------------------------------------------------------+
#property copyright "Copyright © 2004, MetaQuotes Software Corp."
#property link "http://www.metaquotes.net"

#property indicator_chart_window
#property indicator_buffers 2
#property indicator_color1 Blue
#property indicator_color2 Red
//---- input parameters
extern int ADXcrosses = 14;
//---- buffers
double ExtMapBuffer1[];
double ExtMapBuffer2[];
//----
double b4plusdi, b4minusdi, nowplusdi, nowminusdi;
int    nShift;   
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int init()
  {
//---- indicators
    SetIndexStyle(0, DRAW_ARROW, 0, 1);
    SetIndexArrow(0, 233);
    SetIndexBuffer(0, ExtMapBuffer1);
//----
    SetIndexStyle(1, DRAW_ARROW, 0, 1);
    SetIndexArrow(1, 234);
    SetIndexBuffer(1, ExtMapBuffer2);
//---- name for DataWindow and indicator subwindow label
    IndicatorShortName("ADXcrosses");
    SetIndexLabel(0, "ADXcrUp");
    SetIndexLabel(1, "ADXcrDn"); 
//----
    switch(Period())
      {
        case     1: nShift = 1;   break;    
        case     5: nShift = 3;   break; 
        case    15: nShift = 5;   break; 
        case    30: nShift = 10;  break; 
        case    60: nShift = 15;  break; 
        case   240: nShift = 20;  break; 
        case  1440: nShift = 80;  break; 
        case 10080: nShift = 100; break; 
        case 43200: nShift = 200; break;               
      }
//----
    return(0);
  }
//+------------------------------------------------------------------+
//| Custor indicator deinitialization function                       |
//+------------------------------------------------------------------+
int deinit()
  {
//----
    return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int start()
  {
    int limit;
    int counted_bars = IndicatorCounted();
//---- check for possible errors
    if(counted_bars < 0) 
        return(-1);
//---- last counted bar will be recounted
    if(counted_bars > 0) 
        counted_bars--;
    limit = Bars - counted_bars;
//----
    for(int i = 0; i < limit; i++)
      {
        b4plusdi = iADX(NULL, 0, ADXcrosses, PRICE_CLOSE, MODE_PLUSDI, i + 1);
        nowplusdi = iADX(NULL, 0, ADXcrosses, PRICE_CLOSE, MODE_PLUSDI, i);
        b4minusdi = iADX(NULL, 0, ADXcrosses, PRICE_CLOSE, MODE_MINUSDI, i + 1);
        nowminusdi = iADX(NULL, 0, ADXcrosses, PRICE_CLOSE, MODE_MINUSDI, i);  
        //----
        if(b4plusdi < b4minusdi && nowplusdi > nowminusdi)
            ExtMapBuffer1[i] = Low[i] - nShift*Point;
            Alert ("Cross UP");
            
        //----
        if(b4plusdi > b4minusdi && nowplusdi < nowminusdi)
            ExtMapBuffer2[i] = High[i] + nShift*Point;
            Alert ("Cross DOWN");
            
      }
//----
    return(0);
  }
//+------------------------------------------------------------------+