The sprite kit nodes can't actually be removed from parent - ios

Question

I have made 30 bullets with a mutableArray to reuse them.
for var i = 0; i < 30; i++ {
var bulletTmp = SharedAtlas.getInstance().getSpriteNode(SKSpriteType.bullet)
bulletTmp.physicsBody = SKPhysicsBody(rectangleOfSize: bulletTmp.size)
bulletTmp.physicsBody.dynamic = true
bulletTmp.physicsBody.categoryBitMask = bulletCategory
bulletTmp.physicsBody.contactTestBitMask = enemyCategory
bulletTmp.physicsBody.collisionBitMask = enemyCategory
moveBulletToTop = SKAction.moveToY(self.frame.height, duration: NSTimeInterval((self.frame.height - plane.position.y) / 400.0))
bulletGroup.addObject(bulletTmp)
}
The bullets is their parent SKNode
bullets.runAction(SKAction.sequence([SKAction.waitForDuration(1.5), (SKAction.repeatActionForever(SKAction.sequence([SKAction.waitForDuration(0.05),SKAction.runBlock({
var newBullet:MGSpriteNode!
if self.bulletIndex < 29{
self.bulletIndex++
}else{
self.bulletIndex = 0
}
newBullet = self.bulletGroup.objectAtIndex(self.bulletIndex) as MGSpriteNode
newBullet.removeAllActions()
newBullet.removeFromParent()
print(self.childNodeWithName("bullets").children.count)//max value keeps 30
newBullet.runAction(self.moveBulletToTop)
newBullet.position = self.plane.position
newBullet.position.y += self.plane.size.height * 0.5
self.childNodeWithName("bullets").addChild(newBullet)
})])))]))
The question is: I have remove from parent after the bullet moves for a while. But the nodes number on the screen is keep increasing. The children of bullets always be 30 . If I move all of the bullets, everything will be OK. But where are the nodes? Had they actually been removed?