A while back my power was out for a couple of days and I was able to keep my tank alive with one of these cheap inverters . I did have three cars that I rotated the batteries out of to charge them.....but my 29 gallon low tech reef survived. I was kind of astonished. But I wanted to let y’all know that for $12 or so, you could save those smaller tanks.
https://slickdeals.net/f/11138199-300w-vehicle-power-110v-ac-inverter-w-3-1a-dual-usb-adapter-12
https://slickdeals.net/f/11138199-300w-vehicle-power-110v-ac-inverter-w-3-1a-dual-usb-adapter-12