Although I haven't had any tragedisasters like yours, I'm arriving at what appears to be the same place that you are ... lowtechtown.
I've had the co2 shut off to my 180 and 55 gal tanks for about 5 days now. When I shut off the co2, I also stopped my EI dosing to both tanks.
The 55g has 2wpg (2 x 55 watts) over it which are lit from 9a-9p.
The 180g has 1/2 wpg (2 x 55 watts) from 9a-9p with another 1 wpg (2x96 watts) added from 11a-2p.
The 180 is on an "autowaterchange drip" of ~100-110 gal/wk and I'm changing about 1/3 of the water in the 55 every Sunday.
The only significant change I've seen since I stopped the co2/ferts is that the GDA in the 180 has quit regrowing. The walls have remained virtually clean for the past week.
After I finish my waterchanges today, I plan on dosing both tanks with my regular EI dose ... and that's all for the week.
I think it'll be interesting to see if things remain looking good or if it all crashes around my ears as a result of the discontinuing of co2/ferts ... stay tuned ...