The nozzles snap open and you can clean them and the lines coming from the pump. In your area people just use plain water in the reservoir and the water turns all slimy, the slime plugs up the pump, the lines and the nozzles. If you can hear the pump running then the sytem is probably clogged up. Blowing air through the system will maybe solve it for a short while but the tank should come out and be cleaned thoroughly as well as the lines and nozzzles. The nozzles are not cheap and it is best to fix what you have, there is little to go wrong with them except for the heater and I am sure you have no need for that.
You adjust the nozzzles by sticking a pin in the hole and swivelling the nozzle to the best position, the nozzle is a ball shape.