Mines off by an 1/8", but 3/4" of an inch is a lot. I agree, but don't drain it. Do a 50% PWC
, put 25% in buckets and your fish should be fine for the time it'll take to adjust.
Use a crow bar (some kind of lever) and raise the low end till you're level. Then use your allen wrench to adjust the feet to the floor. If they don't extend that far use something solid to fill the space (btw floor & feet).
Refill and you're set.