You should just remove the fish into a bucket and get out all of the water you can and top up with fresh water, then net the fish back in. It is very hard to get a reading of 5.0 down to 0 without doing multiple 80-90% water changes. You can do multiple water changes in a day without hurting anything as long as you dechlorinate the water and roughly match the water temperature (better being cooler than warmer).
I hate to say I told you so but I warned you about adding more fish while going through a fish-in cycle!
Good luck and keep changing your water until you get everything down to 0 (apart from nitrate).