I am writing an app in threes for a set of particles, I want to include collision between the particles. It seems it only check for collisions once - three.js

Question

It seems it only check for collisions once and particles loose speed. If anyone has an advice...
function animate() {
var elapsedTime = clock.getElapsedTime();
particlesGeometry.attributes.position.needsUpdate = true;
const paso = 1.5;
for (let i = 0; i < count; i++) {
const i3 = i * 3;var k = 0;
const x = particlesGeometry.attributes.position.array[i3 + 0];
const y = particlesGeometry.attributes.position.array[i3 + 1];
const z = particlesGeometry.attributes.position.array[i3 + 2];
for (let j=k; j < (count); j++){
const l = 3 * j;
if (l==i3){continue;}
var posx = x - particlesGeometry.attributes.position.array[l + 0];
var posy = y - particlesGeometry.attributes.position.array[l + 1];
var posz = z - particlesGeometry.attributes.position.array[l + 2];
var dist2 = Math.pow(posx,2)+Math.pow(posy,2)+Math.pow(posz,2);
var velMod1 = Math.sqrt(Math.pow(vel[l+0],2)+Math.pow(vel[l+1],2)+Math.pow(vel[l+2],2));
var velMod2 = Math.sqrt(Math.pow(vel[i3+0],2)+Math.pow(vel[i3+1],2)+Math.pow(vel[i3+2],2));
var erre = [posx, posy, posz];
var doterre = erre[0]*erre[0] + erre[1]*erre[1] + erre[2]*erre[2];
var doterreN = Math.sqrt(doterre);
var erreMod = [erre[0]/doterreN, erre[1]/doterreN, erre[2]/doterreN];
if (dist2 <=(velMod1+velMod2)*.05){
var proy1 = erreMod[0]*vel[l+0]+erreMod[1]*vel[l+1]+erreMod[2]*vel[l+2];
var proy2 = erreMod[0]*vel[i3+0]+erreMod[1]*vel[i3+1]+erreMod[2]*vel[i3+2];
vel[l + 0] = vel[l + 0] - proy1*erreMod[0];
vel[l + 1] = vel[l + 1] - proy1*erreMod[1];
vel[l + 2] = vel[l + 2] - proy1*erreMod[2];
vel[i3 + 0] = vel[i3 + 0] - proy2*erreMod[0];
vel[i3 + 1] = vel[i3 + 1] - proy2*erreMod[1];
vel[i3 + 2] = vel[i3 + 2] - proy2*erreMod[2];
particlesGeometry.attributes.color.array[i3+0] = 1;
particlesGeometry.attributes.color.array[i3+1] = 1;
particlesGeometry.attributes.color.array[i3+2] = 1;
particlesGeometry.attributes.color.array[l+0] = 1;
particlesGeometry.attributes.color.array[l+1] = 1;
particlesGeometry.attributes.color.array[l+2] = 1;
}
}
k++;
if (x>=0 || x<=-5){vel[i3+0]=-vel[i3+0]}
if (y>=5 || y<=-5){vel[i3+1]=-vel[i3+1]}
if (z>=5 || z<=-5){vel[i3+2]=-vel[i3+2]}
particlesGeometry.attributes.position.array[i3 + 0] = x + vel[i3+0]*paso;
particlesGeometry.attributes.position.array[i3 + 1] = y + vel[i3+1]*paso;
particlesGeometry.attributes.position.array[i3 + 2] = z + vel[i3+2]*paso;
}
Paso is the step. What I did was to invert the velocity component of the colliding particles along the vector that joins the particles. First I've tried with the dot function for dot product from mathjs but it was too slow so I've coded the dot products, mainly for normalization. The idea is the collision condition is checked for every pair of particles once.
dist2 <=(velMod1+velMod2)*.05
That means the square of the distance between particles must be less than or equal to the sum of their velocities times the step. That latter is in order to avoid particles to oscillate in the collision zone.
In order to check for collision events I've painted the particles that collided on white. The number of white particles should rise as time elapses but that is not the case when running the program.
particlesGeometry.attributes.color.array[i3+0] = 1;
particlesGeometry.attributes.color.array[i3+1] = 1;
particlesGeometry.attributes.color.array[i3+2] = 1;
particlesGeometry.attributes.color.array[l+0] = 1;
particlesGeometry.attributes.color.array[l+1] = 1;
particlesGeometry.attributes.color.array[l+2] = 1;
Thank you.
I've tried to write the double iteration in different forms, the same for the vector operations but the results were funny.