I've had upside down cats in my big tank for a few moths now and they have been fine, coming out when fed etc. Then i added a rainbow cichlid and all seemed fine for a week or so, then one evening he was being really aggressive to the cats to get at the algae wafers. Since then i haven't really seen the cats except for their tails sticking out of hiding places. Do you think they're allright, and will they come out again soon? Or should i worry about the rainbow being a bully?

Probably find the usual will happen , cichlids take the dayshift, catfish take the nocturnal. Cichlids usually only feed in the day and most cats whether diurnal, nocturnal or non specific all tend to like night feeding anyway, their sensory kit makes it easy.

Just do day and night feeds tailored for each group.Sometimes cats and cichlids get on, sometimes they don't but the day/night shift is usually taken advantage of to keep confrontation to a minimum.

A catfish running into a cichlids territory will always be in for a bit of flack as they will be considered a threat to nestsites and fry and are often warned to keep their distance even when eggs and fry arent around. Feeding competition can happen with almost any species that has the wit to defend a foodsource, my uaru for example are very snotty about feeding times, but again take advantage of night feeds.

Its probably a good idea cichlids do defend their foodsources against cats anyway, its very easy for a catfish to glutton feed and deny other fish feeding opportunities. The oxydoras and the uara have standoffs primarily because he just hoovers up all the food and they will want some. You can try diverting tricks like blanched lettuce leaves. Rainbow cichlids will pick at them leaving the cats hopefully free to go for pellets etc.

With upside down cats they will feed on micro-organisms too , so a day old bit of lettuce thats started to fall apart a little can be a browsing area and the cichlids only want it while its fresh. Have to watch your nitrate levels if leaving lettuce in more than a day though.