The water pressure in the shower has been weak for the past few weeks. The water pressure from the bath faucet however is normal. I have a specific faucet with a shower switch. when I turn the water on and pull the shower switch up the pressure is ok but after just a few minutes it becomes weak. I noticed that if I push the switch down (the water switches to faucet when the switch is down) then pull it up again the shower pressure goes back to normal, then again becomes weak in a few minutes. If I keep doing the switch thing (switching to faucet then to shower again) the shower pressure is fixed only for a couple of minutes. I do notice brownish color has formed on the shower head.
I was wondering if it's the shower head causing it and needs to be replaced or if it's the water mixer (switch mechanism) is broken and needs replacement.
Here is a picture