Did you pour a "mud slab," before pouring the floor?

Is there a water seal below the floor and walls?

The exposed re-bar in the picture also looks as though you have a large "cold joint," in that portion of the pour?

With a water seal in place prior to mud slab or wall pours it insures that external migration of water will not affect the pour and set concrete in the future. sometimes called a vapor barrier.

When you made your floor slab pour was it done in conjunction with the walls? The joint between the floor and the walls should have had a water seal as well.

With the blow out or void along with the cold joint it should all be hammered out. Once completed, re-form and re-pour. Insure that "all," re-bar is clean and free of rust prior to pour.

What size vibrator did you use? I would think that 3/4" -1" dia. would do nicely. don't let the vibrator rest in place more than a few seconds and make sure it begins from the first moment of the pour as as the height rises the ability of the vibrator to penetrate the concrete decreases. Over vibration can cause blow outs as is possibly one of the reasons for the wall failure.

Plasticizer or super plastiziser does not guarantee the water retention qualities of the mix, but allows the mix to set or be held for longer periods depending on mix temperatures and other variations.

If its wrong to begin with, my advice is do it right. There's no substitute.

You will no doubt be tiling this pool later. Floor and wall variations will cause costly special cutting of tiles to fit error locations.

Offered as an alternative to other suggestions.

Good luck.