A few things I do that has helped out when using OA for rust removal from parts ( I haven't done a frame yet ),

If I only have a few parts that need attention I use distilled water instead of tap water, using a tub that is 2 gal or less.

Anything more then a few gallons of water I use Tap, but I also use a hot/warming tray/plate under my tub ( Something I read somewhere that stated keeping the OA warm works better ) . I also have a little water pump that was a replacement for a table top fountain, it has suction cups for feet and I stick it to the tub for circular flow. The pump helps with sediment build up ( yellowing ) from using tap water and/or mixing problems.

Glenn