We should target getting the dissolved oxygen at 80% or more of saturation. One way to do that is by pumping air into the pond and filters. A good rule of thumb (reference
Koi 2 Kichi) is to pump at least 40L into each 1000UK/1200US gallons.
So if we do some simple math... 7500 divided by 1200 = 6.25, S0 6.25 x 40L = 250L. So you should plan to pump around 250L into your pond system. Two 120L should do the trick. For our 10,000 pond I use two 120L and two 80L.
It seems as if the delivery is a problem. Folks would typically use:
-air domes on BDs
-fluid bed bio filters
-air stones in matting chambers
-air stones in pond
Since the pond does not seem to be able to do air domes....that leaves the other options for delivery. Please don't tell us you are using a pressurized filter system.
