Gerg:
If this was my pool, I would take my shop vac (I also have extensions) enough to get down 8' and place on the blower side. I would carefully lower the blower into the water, add the acid and use the blower to mix the water. This should work, but I would try it first. Do not know what type of cover you have.
The reason why I have extensions is that the mason kicked some 3/4" rocks in the pool when he poured the cement and I needed a way to grab them without diving in to really cold water. It took a while as the water filled the Rigid wet vac, but you will be using a blower sude. Hopefully you have a blower. The extension unfortunately are like $40 if I remember correctly.
The other option is to purchase a 10' - 2 inch or 1.5 inch PVC and with the use of blow thru plugs and an air compressor to move water around on the bottom of the pool.