Hi Ryan,
The only places I have seen Discus kept at temps lower than 28C was at a LFS. The Discus there are kept in these tanks for relitavely short periods of time.
Discus wont die immediately from being kept lower than 28, they will be more susceptible to disease and will not show their beautiful colours.
The fact is that where Discus are caught, the temperature almost never strays far from 30-32C and Discus have evolved to deal with the lower oxygen in such water.
There is nothing to say that you cant keep Discus with the fish you mention, IF you are very careful about what fish you buy and how they have been kept beforehand.
You should however accept the fact that you will lose some Discus. Only keep Discus with other fish if they have been kept like this in the shop.
A good LFS will keep the Discus alone or with tetras, at the front of the shop where people will pass by regularly. Be cautious if the Discus are kept at the back or are hidden away in darkend tanks or conversely are crammed in with a wide variety of species in a busy community tank.
If Discus are kept like this, the person selling them probably has little understanding of Discus and how they should be kept. Their fish and advice should be taken with a 'pinch of salt'.
Buy a group of Discus no smaller than 4", they should have a forehead as wide as the mouth region, any pinched look could mean parasites and disease.
They should look almost perfectly round, if they look slightly longer than tall, they may have had stunted growth, an indicator of disease.
They eye should be in good proportions to the body, if it looks slighlty bigger than it should, this is also an indicator of poor health and stunted growth.
Check they are breathing from both gills and at regular intervals. If they are not, it is an indicator of gill worms or other parasites.
Never buy a Discus that does not use all of its fins all of the time, check them all.
The disadvantages of keeping Discus with other fish are:
They are generally timid and wont compete for food. This may lead to starvation and death due to disease.
They are difficult to medicate. When kept at the correct temperature, they are fairly resistant to disease when settled in. Fish kept with Discus should not be treated in the Discus tank as Discus dislike any excess or foreign dissolved chemicals.
Diseases which other fish are immune to may attack Discus and you may never know the source. Because of the nature of their habitat, Discus may never have been exposed to some parasites and diseases that other fish have evolved defences against. Your Discus could keep dying in an otherwise healthy appearing tank.
Discus have a water preference that some effort should be made to duplicate.
You can keep Discus in most types of water after a long acclimatization, but they will never 'fit in' to a general community tank. Making an effort to give them the water they need has many many benifits for the fish and you that you lose when you try to get the fish to adapt to your water.
There are as many opinions on how to keep Discus as there are varities. I believe in giving the fish what they need. Discus have been kept in a wide range of circumstances but the only group of people who can consistently keep Discus healthy and colourful are those who know and can duplicate their natural habitat.
I think this is a very wise principle.
For every person who says their Discus do fine in pH 8 and live happily with barbs, angels and gouramis, there are dozens more who failed miserably and who contribute to the myth that Discus are delicate. They are not, they just have their own requirements.
I think of Discus like I do marine fish, when going for marine fish, you are careful to give them the water similar to that which they come from, the same should be true for Discus and it will go a long way to keeping them healthy.
Ken
HI,
Discus scare me 
