The h2o2 is killing your aquashield bennies so you have to stop running it in your res, but you can wash/clean with it between res changes. You also need to dechlorinate or use R/O water from the grocery store or whatever because that will probably kill the aquashield too. 55ml in 4 gallons is waste of money, 20-25 ml is fine. Continue to add it to the res two or three times a week throughout the entire grow. I don't know what system you are in, but in DWC h2o2 rarely does dick, especially once you have an established problem. I have had and beaten root rot with aquashield on several occasions but you have to be sure you don't kill it... or brew up stronger tea that can survive the chems (heisenberg sticky thread in dwc forum). Each time I got slimed it was due to fucking up the aquashield or not using enough or often enough.
Make sure your aquashield isn't expired... look in the bottle and see if you see mush chunks floating around. Smallish dark black specs is normal. This is something almost everyone goes through that does some form of DWC, but it is simple and cheap to fix. Make sure you have an air pump, 100% light proof, 70* water... use a gatorade cooler or wrap your bucket in 3 layers of silver bubble wrap (reflectix - home depot) and give it a 1L bottle of ice once a day. I don't know what kind of set up you have, but adapt the principles to fit your needs.