Which shampoo do i need to use after the semi permanent dye has washed off?

I am a 36 year old male. I got dyed my hair with a semi permanent dye about a month back. After about a month of washing my hair the original color of my hair has come back. Lately i have been experiencing heavy hair loss especially when i shampoo my hair (i use Nioxin System 2). I am wondering if i need to use a shampoo thats specifically for color treated hair or not.. since the color has washed away already and its not dyed anymore? or should i just use a regular shampoo..? I dont know why my hair has been falling so much.i thought it was the chlorine in the water, so I switched to a showerhead with a anti-chlorine filter... but it hasnt helped much. Any suggestions?