Originally Posted by Skooter
I was also going to get some Discus because I found a guy who will them for like $10 each (juveniles)..So if I have a 55gl tank and am only running 15 Neons and a herd of Ruby shrimp are you saying that they will not thrive in the same water conditions?
Each fish species has a "preferred" set of water parameters, which includes hardness, pH and temperature. This range is determined by nature. Some fish appear to be more adaptable than others respecting hardness and pH, and some are not. When it comes to temperature though, each species has a range in which they will do much better. Their metabolism is geared for certain temperatures, and while minor fluctuations that are temporary are usually OK, permanent conditions will most likely result in difficulty for the fish. This can be as simple as stress [which however weakens the immune system causing more trouble health-wise] but more often involves issues with digestion, respiration, behaviours, and so forth.
In our profiles, the safe temperature range is given for each species. Discus must have warm water, certainly never below 80F and preferably above that. Neon tetra by contrast will "burn out" at such high temperatures. Cardinal tetra is much more suitable with discus since cardinals can manage quite well at higher temperatures. Most corydoras species also have difficulty above 80F, with a few exceptions.
Have a read of our profiles, all these fish are included. Click on the shaded name for that fish's profile.