Algae where it connects to the RV.. Well Algae needs moisture, So you must need a new hose washer on that connection.
Bleach will kill it,Soak the end and fittings for like a minute then rinse well
Mix 1 ounce (shot glass?) of bleach in 2 gallons of water and blow out the hose (Drain it) hold up the "Far end" at least an few inches, then take and using a funnel pour the water through the hose. Lower the "near end" till bleach water backflows.
Then lift it up to the park faucet, hook it up and let it blast the solution out of the hose.
You might also wish to sanatize the RV system.
"The mix here is 1/4 cup bleach per 5 gallons. Fill the tank (Adding bleach when half full) and run through all lines.. Then drain and flush (Clear water)
Then flush with baking soda (1/2 cup mixed in water till it disloves add to tank when half full, fill flush and drain.
Then clear water flush again
Then fill and use
If you do this you might add via the quick fill (Using the method I described above for sanatizing the hose)