ML I would argue that by leaving all the large HSB in the kids pond you would be unknowingly changing the test. It would also be wasting the potential of the HSB and risking the kids pond's contents.

The test was to see how the GG would do in a normal pond (offspring and growth etc). If you leave all the big HSB in the pond it will soon not resemble a normal pond. A normal pond has predators of all sizes (with most being small) to pressure the yoy GG not just a bunch of big predators which may not waste energy on hunting yoy GG.

Leaving all the big HSB in the kids pond IMO would be a waste of their potential and could result in it maxing carrying capacity soon with all the negatives that carries with it as well.

I would move all but a few of the HSB and replace them with some new smaller ones realizing that the few remaining big HSB may eat a few of the small ones. That would keep the test nearer to a normal pond test with multi-sized predators.