Mikrogeouphagus ramirezi (Blue, Gold and Electric blue rams) need to be kept at temperatures of 28-32°C as this is the temperature at which they are found in the wild
It is very rare to come across an environment where the temperature is limited to a 4° range, the most common areas where this occurs tend to be at the bottom of the oceans. If you do not believe me, look up the air temperature of the area where wild rams live: the average summer (air) temperatures tend to be in the 28°C range, but winter temperatures fall into the 22-23°C range, while average throughout the year is around 25°C.
Now to water temperatures: water in full sunlight will heat up to 32°C, 33°C or even higher without too much of a problem from 28°C.. but what happens at night? In the space of a few hours after sunset, the temperature of the water will have already dropped by a few degrees.. and over winter?
So where did you get the 28-32° figure? Unfortunately I can't get hold of the original paper describing them, but that - at least to me - would indicate that the fish were collected in the summer.
Now I have a proposal for you: you say that you are interested in biology, plants etc.. and I happen to have a friend who is leading a fish collecting expedition next August into the river Nanay area.. I know not quite Orinoco, but I hear that it is, nevertheless, stunning and the trips includes visiting exporters facilities. The cost of the trip is expected to be about £1400 including flights from Gatwick, or £2000 including flights and freight for the fish you catch. The main fish on the agenda will be Apistos and the non-native ‘Nanay’ discus. I would be going myself, but money matters are not allowing me the oportunity, so I am only getting fish. But if you are able to get that much cash together and are at least 16 years old by the time of departure, then I would strongly recommend the trip.
fail to do this and you face either of these 3:
Hexamita, Slow Immune response and Slow digestion.
I have kept a number of wild caught and a number of German bred ram pairs at various temperatures over the years, ranging from 22°C all the way to 30°C. None of the fish I had ever suffered from any symptoms relating to the diseases you mention above.. in fact, I have never seen any sign of disease in my fish at all. I suspect that good care, water quality and appropriate food have more of an effect on the health of the fish then the temperature.
PH and GH also play an important factor, PH should be between 5-6.5 and the GH no more than 10 degrees.
Agreed that water quality is very important.