If you put 175 psi into your system and only got tiny bubbles at the diffusers...you most likely have a kink or clog in the lines/diffusers, or a break that is letting all you air escape (maybe underground?)
When I deadhead my pump it really makes some odd fluttering noises that are an obvious sign that something is not right. If your pump sounds normal while hooked up to the system and no bubbles are coming out...my bet is that you have a massive leak underground, but not underwater. If it where your pump, the compressor air test would have shown some results.
What kind of pump is the Kasco? Rotary Vane, Piston, Diaphragm, etc.
A pressure gage, as mentioned, is a great troubleshooting tool to have.
Side Note: I would bet that the system is not made to handle that type of pressure (175 psi). Please reconsider putting that kind of air pressure to it again. I would recommend using an air line pressure regulator in the future for that kind of testing. Set the regulator to what the system is designed for (about 10 psi should be safe, maybe as high as 20). 175 psi could be enough to burst something.
