I had a problem like yours a couple years ago when restarting one of the diffusers that was shut down for the winter. What ever the problem was, between the diffuser, the check valve and 200 feet of hose, I can only guess.
Here's what solved the problem...
I put a portable air tank in place of the pump, and slowly increased the pressure. problem solved, not another issue since.
I installed a barb on one of my air nozzles at shop. Clamped hose to nozzle and run 120psi through hose from a 90 gal compressor for several minutes at a time, let compressor catch up, do it again.. I think I need to try the hydrogen peroxide or new hose. Hope I don't need to replace weighted line every 3-4 months.
