G'day mate. When you fill do aggressively agitate the water as it enters your storage barrel? 1 of the contestants (i think Adam or Jeep, but not sure atm) on the grow out challenge showed images using a spray nozzle of some sort to rapidly accelerate the gasing off process. I use my finger and spray aggressively as I fill my 55 gal barrel with warm tap water and then aerate with a single stone for 3 hours and then do my wc. My gosh are happy healthy and spawning every 4 days or so...
HTH