Fish movement in a fish tank

I am programming a aquarium and I'm having trouble with the movement of the fish. The plan was moving the fish with for loops to the random location set by random variables.

void EntityControl::movementController(std::vector<Fish*> * fishInputVector)
{
    while (true) {

    for (auto fish_ptr : *fishInputVector) {
        //fix this
            for (auto fish_ptr2 : *fishInputVector) {
            //random location
            unsigned int x = rand() % xContainer;
            unsigned int y = rand() % yContainer;
            unsigned int z = rand() % zContainer;

            //if (!CheckCollision(fish_ptr, fish_ptr2)) {
                unsigned int xPos = fish_ptr->getX();
                unsigned int yPos = fish_ptr->getY();
                unsigned int zPos = fish_ptr->getZ();

                 }

            //}
        }
    }
}

this didn't work so I tried a lot of different things but I was not succesful in making it work. I also have a collision detector which detects when the fish are 1 x/y/z away from each other. Another action should be taken when this happens.

bool EntityControl::CheckCollision(Fish * fishInput, Fish * fishInput2)
{
    //collision true/false
    bool collision = false;

//collision detectors
bool xCollision = false;
bool yCollision = false;
bool zCollision = false;

//fishInput
unsigned int xOriginal = fishInput->getX();
unsigned int yOriginal = fishInput->getY();
unsigned int zOriginal = fishInput->getZ();

//fishInput2
unsigned int xEntity = fishInput2->getX();
unsigned int yEntity = fishInput2->getY();
unsigned int zEntity = fishInput2->getZ();

//directions, (triggerBox)
if (xOriginal - 1 == xEntity || xOriginal + 1 == xEntity || xOriginal == xEntity) { xCollision = true; }
if (yOriginal - 1 == yEntity || yOriginal + 1 == yEntity || yOriginal == yEntity) { yCollision = true; }
if (zOriginal - 1 == zEntity || zOriginal + 1 == zEntity || zOriginal == zEntity) { zCollision = true; }


//returns true if all 3 directions are true
if (xCollision && yCollision && zCollision) { collision = true; }

return collision;
}

Both are in the same class. I am looking more for a general direction than a solution. But both are fine.

problem summary Moving every fish in a random direction without static movement and calling the checkCollision constantly so it can check for collision.