Evolved raises a good point about flow. Again, just my opinion here, but the flow needs to be stronger and more random. A 55 is usually 4 ft and I would guess your 125 to be at least that. Even if your mp40 can push the length of the tank the other power head probably cannot offset it very well. I would suspect you have a singular flow stream. When you put food in does it all go in the same direction or does it flow in all different directions?
All the other points about light and water 'readiness' are spot on as well but as far as what is easy and relatively quick I would focus on seeing what can be done about the water movement...
And don't give up. Sps are just really finicky and any moving of them in general can be viewed as a gamble..
Good luck.