Dirty toilet water

All of our sinks and toilet run clear water EXCEPT our 2nd floor toilet. We see dirty water in the toilet every day. We cleaned the tank but the water in bowl is still dirty. Just the 2nd floor toilet.
I read somewhere that we might need to clean the vent and pipe from the roof by running garden hose and water down it. Can someone confirm that this might be a solution before I go up there? Any other possibilities of why we have this problem upstairs?
Thank you

What do mean by dirty?
Is the water in the tank and/or bowl discolored?
Or do you have stragglers in the bowl after you flush?
Water was to get to the tank before the bowl.
Could be you have a iron pipe nipple in the supply to toilet that is causing discoloration.
I doubt very much that it is a venting problem. Although venting will effect how it flushes.