Canna D Block is a nutrient additive designed to prevent the buildup of salts within irrigation lines and spray heads. It should be added right from the start of the growing cycle at 10ml per 100ml of nutrient solution - if used like this then you will never have to worry about blockages ever again.
Add to the nutrient solution at 10ml per 100 litres. Between cycles, you can use it to flush the entire system, for best results when doing this lower the PH to 5.2 and run for several hours.
Canna D Block will also help prevent the build-up of precipitant in nutrients tanks where the solution is standing for a long time.