CAEmitterLayer works for a while, then stops diplaying. Objective C

Question

I have added some fireworks to an app. The emitters work a few times, then stops displaying.

Here is the Objective C code

in the .m

- (void) viewDidLoad {
 
  [super viewDidLoad];


  [self setupEmitter];
  [self setupFireWorkEmitterCells];

 }



-(void) setupEmitter{
emitterLayer = [CAEmitterLayer layer];
emitterLayer.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height-100);
emitterLayer.position = CGPointMake(self.view.frame.size.width/2, self.view.frame.size.height/2);

emitterLayer.emitterShape = kCAEmitterLayerPoint;

emitterLayer.backgroundColor = [[UIColor colorWithRed:0.0 green:0.2 blue:0.2 alpha:0.500] CGColor];

emitterLayer.emitterPosition =  CGPointMake(self.view.frame.size.width/2, self.view.frame.size.height);

emitterLayer.emitterSize = CGSizeMake(30, 30);

emitterLayer.emitterMode = kCAEmitterLayerOutline;
emitterLayer.renderMode = kCAEmitterLayerAdditive;

emitterLayer.needsDisplayOnBoundsChange = YES;
emitterLayer.delegate = self;

[self.view.layer insertSublayer:emitterLayer below:BottomBar.layer];

}



-(void) setupFireWorkEmitterCells{


 NSLog(@"setupFirework cellls");

 //============== EMITTER CELL 1 - Parent ==============

 // emitter =  [NSKeyedUnarchiver unarchiveObjectWithFile:[[NSBundle mainBundle] pathForResource:@"Sparks" ofType:@"sks"]];

//Create Cell
 CAEmitterCell *cell1 = [CAEmitterCell emitterCell];

 cell1.name = @"Parent";

 cell1.birthRate = 0.0;
 cell1.lifetime = 2.5;
 cell1.lifetimeRange = 0.0;
 cell1.beginTime = CACurrentMediaTime();
 cell1.velocity = 300.0;
 cell1.velocityRange = 100.0;
 cell1.xAcceleration = 0;
 cell1.yAcceleration = -100.0;
 cell1.emissionLatitude = 0.0 * (M_PI / 180.0);
 cell1.emissionLongitude = -90.0 * (M_PI / 180.0);
 cell1.emissionRange = 45.0 * (M_PI / 180.0);

 cell1.spin = 0.0 * (M_PI / 180.0);
 cell1.spinRange = 0.0 * (M_PI / 180.0);

 cell1.scale = 0.0;

 cell1.scaleRange = 0.0;
 cell1.scaleSpeed = 0.0;
 cell1.alphaRange = 0.0;
 cell1.alphaSpeed = 0.0;
 cell1.color = [UIColor colorWithRed:255.0/255.0 green: 255.0/255.0 blue: 255.0/255.0 alpha: 1.0].CGColor;
 cell1.redRange = 0.9;
 cell1.greenRange = 0.9;
 cell1.blueRange = 0.9;





 //============== EMITTER subCELL 1 - Trail ==============

 //  UIImage *image1_1 =   [UIImage imageNamed:@"Spark"];//.CGImage;

 CAEmitterCell *subcell1_1 = [CAEmitterCell emitterCell];

subcell1_1.contents = (id) [[UIImage imageNamed:@"FW-white.png"] CGImage];
subcell1_1.name = @"Trail";
subcell1_1.birthRate = 145.0;
subcell1_1.lifetime = 0.5;
subcell1_1.beginTime = 0.01;
subcell1_1.duration = 1.7;
subcell1_1.velocity = 80.0;
subcell1_1.velocityRange = 100.0;
subcell1_1.xAcceleration = 100.0;
subcell1_1.yAcceleration = 350.0;
subcell1_1.emissionLatitude = 0.0 * (M_PI / 180.0);
subcell1_1.emissionLongitude = -360.0 * (M_PI / 180.0);
subcell1_1.emissionRange = 22.5 * (M_PI / 180.0);
subcell1_1.spin = 0.0 * (M_PI/ 180.0);
subcell1_1.spinRange = 0.0 * (M_PI / 180.0);
subcell1_1.scale = 0.5;
subcell1_1.scaleRange = 0.0;

subcell1_1.scaleSpeed = 0.13;
subcell1_1.alphaRange = 0.0;
subcell1_1.alphaSpeed = -0.7;
subcell1_1.color = [UIColor colorWithRed:255.0/255.0 green: 255.0/255.0 blue: 255.0/255.0 alpha: 1.0].CGColor;
subcell1_1.redRange = 0.0;
subcell1_1.blueRange = 0.0;
subcell1_1.greenRange = 0.0;

    
//============== EMITTER sebCELL 2 - Fire Work ==============

CAEmitterCell *subcell1_2 = [CAEmitterCell emitterCell];


subcell1_2.contents = (id) [[UIImage imageNamed:@"FW-white.png"] CGImage];
subcell1_2.name = @"Firework";
subcell1_2.birthRate = 20000.0;
subcell1_2.lifetime = 15.0;
subcell1_2.lifetimeRange = 0.0;
subcell1_2.beginTime = 1.6;
subcell1_2.duration = 0.1;
subcell1_2.velocity = 190.0;
subcell1_2.velocityRange = 0.0;
subcell1_2.xAcceleration = 0.0;
subcell1_2.yAcceleration = 80.0;
subcell1_2.emissionLatitude = 0.0 * (M_PI / 180.0);
subcell1_2.emissionLongitude = 0.0 * (M_PI / 180.0);
subcell1_2.emissionRange = 360.0 * (M_PI / 180.0);
subcell1_2.spin = 114.6 * (M_PI / 180.0);
subcell1_2.spinRange = 0.0 * (M_PI / 180.0);
subcell1_2.scale = 0.1;
subcell1_2.scaleRange = 0.0;
subcell1_2.scaleSpeed = 0.12;// was.09
subcell1_2.alphaRange = 0.40;
subcell1_2.alphaSpeed = -0.7;
subcell1_2.color = [UIColor colorWithRed:255.0/255.0 green: 255.0/255.0 blue: 255.0/255.0 alpha: 1.0].CGColor;
subcell1_2.redRange = 0.0;
subcell1_2.greenRange = 0.0;
subcell1_2.blueRange = 0.0;

 cell1.emitterCells =  [NSArray arrayWithObjects:subcell1_1, subcell1_2, nil];

emitterLayer.emitterCells = [NSArray arrayWithObject:cell1];


}

The code I use to trigger the effect is

I connect the action below to a button:

 -(IBAction)StartFW {

 [emitterLayer setValue:[NSNumber numberWithInt:1] forKeyPath:@"emitterCells.Parent.birthRate"];

  }

To code I use to stop the effect is

I connect the action below to a button:

 -(IBAction)StopFW {

  [emitterLayer setValue:[NSNumber numberWithInt:0] forKeyPath:@"emitterCells.Parent.birthRate"];

  }

When I trigger the code, by pressing a button, the fireworks work fine, but after a little bit, they will not work. What can I try to solve this?