The thing with pop-eye is, it's often a sign of poor water quality. You may well have treated the symptoms before but without getting rid of whatever is causing it you're likely to have it again. It could also be down to injury or bacterial infection, which has caused fluid to collect behind the eye, pushing it outwards.
Personally I'd keep on top of regular water changes, and treat with the same treatment that you used for your betta if it worked. I'd suggest adding a bit of salt to prevent infection and draw the fluid out but your otos will not appreciate this, so this should be avoided. It might be worth however either moving the affected fish to another tank, or removing the otos for a bit, as otos can be quite sensitive to water treatments. Unfortunately I don't think your 1 gallons will be big enough to maintain pristine water conditions in which to heal the fish.