I agree with Forkfish. The Attwood hull cleaner works great. However, it is cheaper to get "The Works" GREEN bottle at Walmart or a Dollar Tree. It has the same ingredient as the Attwood hull cleaner and CLR. The main ingredient is Oxalic Acid. Do not get the Blue bottle of "The Works". It contains a harsher acid. Try not to get it on your trailer. Be sure to wax your boat after using these cleaners. If you don't, it will just get stained again the next time you use it. I have also used Dollar Tree's version of Oxy Clean. I just put a couple of scoops in a bucket of water & it works very well. It's not harsh like the acid based cleaners and it won't hurt your trailer or carpet. As a matter of fact, it works very well on your carpet & trailer too.
Have a Blessed Day,