I would start at the tank and make sure that water is coming out freely.
Then reconnect the tank and disconnect the outlet to the pump and make sure that is working ok.
Or, where the water goes into the hose reel, disconnect it, take off the fitting and just check the water flow from the bare hose.
Reconnect the fitting. I would then take all the hose off the reel, make up 10 foot of short hose (from spare bits) and again just check the flow with no end fittings. If you get to that stage and it still works ok, it's probably your main hose, pole hose or brush.
Stick the connector on the short hose you made up and attach your pole and brush etc and make sure that all works.
Then you're back to your main hose.
I know it's a bit 'teaching you to suck eggs' but if you're methodical and take your time, you should find the problem.