Geophagus and Discus

I think it would entirely depend upon your choice of Geophagus - certainly not the Brasiliensis, the ones I owned were real terrors...at least the male was!
Some of the species actually live in the wild together, but obviously not "hand in hand" with each other!
Somewhere I have a book about Discus with a picture in it showing what they called "Long-finned" Geophagus species being caught in the nets along with the Discus they were actually fishing for.

My concern would be that even if you tried any of the less agressive Geos and they did actually co-exist there would almost certainly be water temperature issues - at least that would be my guess.
Discus are maintained at such artificially high temperatures to keep parasites at bay - and have been kept like this for so many generations now that this has become the 'norm' for them -but the question would be, could the Geos survive for long enough to become established at the much higher level?
I think it would, if you gave it a try, have to be a case of buying your fish, putting them into a separate tank and build up the temperature - very gradually - to whatever you have your Discus at. Probably over the course of a good few weeks at that. Wild fish could take even longer I should think.

Another thing worth thinking about is the Discus themselves - if, as I suspect, they are adults
they might not take too kindly to newcomers, especially other Cichlids. Sometimes it can be overlooked that they are themselves Cichlids and are very often extremely aggressive and particularly territorial too.

I think that this would require further consideration, try to find a Discus Forum (I think there are a few out there in Cyberspace) and see if anyone there has tried what you're considering - there isn't too much in Fishkeeping that someone somewhere hasn't tried before! You could learn from their experiences - good or bad - which could help you make your final decision.

John

John do you still keep geo's? What ones would you recommend to start with if i can get my hands on them!

Right at this moment I have none, but keep looking out for Acaricthys Heckeli - while not strictly a Geo they are certainly in that species category (well, vaguely).

Some of the more recently-discovered Geos are very nice, I wouldn't mind some of those. I'm going over to UK in the Spring and plan to have a good trawl around the shops in the South East to see what's on offer.

I also like the Geophagus Daemon, but have never kept them - all I ever kept were the Brasiliensis I mentioned before and Jurapari - which unfortunately never did breed...now, both of these have probably been re-classified - as is the way of things, but I'm talking back to the days when all Central American Cichlids were Cichlasomas and all non-Tilapia cichlids from Africa were Haplochromis, I could go on, but you probably see what I mean.

I'll have to try to look out the book you asked about, but it is pretty old (a bit like its owner!). I'm almost certain it was by Herbert Axelrod though, I'll do a bit of searching after I've been shopping.

John
ps, A bit off subject, but how did your Killifish project get on?