Hey Matt, I'm no expert but one thing I haven't heard you try doing has to do with changing your maintenance routine a little and simulating the "rainy season." You might try feeding them their favorite foods quite liberally for a couple of days and skipping their water changes. Then do one of your usual WCs, maybe on the larger side but with water in the mid-70s instead of the usual. (Go ahead and let the tank's heater slowly bring it back up to normal.) I did something like this accidentally when I had a heater fail in my aging barrel, and I think it helped. There may be more advice on this approach if you search old threads.