I agree with Cleancare - the way you're trying to make your pump work is a complete waste of time
The area ratio of 1/2" hose to 1" hose is 1:4
In other words, looking on the end of the hose, the hole in a 1" hose is four times bigger than the hole in a 1/2" hose. Without allowing for slight variations owing to friction etc, a 1" hose will deliver four times as much water in the same time as would a 1/2" hose.
Putting 1/2" hose on a 150lt/min pump is like trying to run your engine starter motor with 10 amp cable - somethings going to give!!