Your doing pretty good....no real catastrophe. I concur with Opie. I use DWC and I have four 14 inch air stones in a reservoir the size of yours.
I use Hygrozyme once a week or sometimes every other week.
I bought a pondmaster ap40 pump which is a deep water pump and can really put out some air.
It pours out the bubbles in five different air stones with power to spare.
If you keep the temps down in your water as much as you can and kick up the aeration you might get by without the Hygrozme.
I put frozen water bottles without the lid off in my res, as the water melts it bleeds into the res and replenishes the res with fresh water.
Good luck and keeps us posted.