I have recently purchased three altums to go into my new 40 gal aquarium. The three of them settled in quickly. I have them nearly three weeks now but last night after I fed them, they started to get quite aggressive towards each other therefore they were not sticking together like they usually do. They were also showing their colours really brightly to each other if you know what I mean. I was wondering is this just because they are getting jealous towards each other over feeding time?
Sound like fairly normal behaviour I am afraid. Angels like all cichlids are territorial, as they settle in to a place they will probably be ok to start but will eventually establish territories, this is probably what is happening. In a big group this is not always a problem, but 3 is a really bad number, you may end up with one pair and and odd one, or three individuals - as long as there is plenty of room you should be ok, but I would suggest getting 3 or 4 more if you have room they may act more as a group, but I would not bet on it.
Paddy is absolutely right. In my opinion these fish need to be kept in groups of at least six to dissipate the aggression. They usually have a bit of a scrap after feeding. I dont know how big your fish are, but they are much better with more room (these fish take up a lot of space when adult) I find that in a large group they are much more sociable and exhibit shoaling behaviour. Sadly, it is difficult to obtain large groups as shops usually only stock them in small numbers due to the high price (and huge mortality). The other difficulty is finding other dithers to cohabit with them, they will try and eat anything that will go in their mouths (and try some that don't quite with dire results!) They are the most spectacular Angel and IMHO well worth all the trouble (I have had them kill each other in a five foot tank!)Good luck!