RO is not 100% pure water. When I decided I needed to soften my water I went with an RO/DI/ This got me pretty close to pure H2O. Because all of the KH is gone, there is very little to hold up the pH. The result of this is it can drop very low. The DI unit removes Ions. Many of us do not think about Ions but we all deal with them if we have a successful tank.
An ion is an atom or molecule with a net electric charge due to the loss or gain of one or more valence electrons. Because the number of electrons no longer equals the number of protons, ions are charged particles. They are crucial for chemical bonding, electrical conductivity, and biological processes.
While a decent RO system can remove between 95% and 99% of impurities etc. and RO/DI system is basically 100%. The quality of the RO membrane is what determines how many things and RO unit can remove. Some membrane can remove nitrate but lesser quality ,membrane may not do so. An RO unit will not help with ammonia or nitrite but other things which it misses may be captured by carbon. My initial unit was three modules carbon-->RO membrane-->DI resin. This gave me pr pretty pure water. While RO water is OK for drinking, DI water is not.
I mixed my RO/DI water with my tap water. Ultimately,when I decided to get a new unit rather than replace modules again I went with a 4 stage which added a sediment filter in fron ot the carbon.
Then there is this:
A Reverse Osmosis (RO) system effectively removes nitrifying bacteria and other microorganisms from water. RO membranes have tiny pores (roughly 0.0001 microns) much smaller than bacteria, which are typically 0.2 microns or larger, trapping them and preventing them from passing into the treated water.
What a DI module will do is to remove both ammonia as ammonium and nitrite from water.
What RO is best at removing is a lot of what contributes to TDS but not everything that does so. And then the quality of the specific RO membrane one has determines how much it can catch. This can mean some of what the palnts and fish need will not be removed.
Also, it makes a difference if one is panting mostly or all aquatic plants or if there are a decent number of land plants whose roots are in the water. These plants take things from the air. They also use ammonium and nitrate. So what quality RO membrane one has can matter in this respect. Plus land plants have access to CO2 which is greater in the air than the water. Land plants ned to support themselves so have sturdier stems, Aquatic plants tend to have a tendency to float and this helps them to get taller without needed massive stem support to preven falling over.
I did not plant my altum tank becase of how stained my water was. This tends to reduce light levels in water. I have seen a number of vids of altums in the wil. Most of the plants one sees are land plants which have become submerged due to the rising levels of the rivers durning the rainy season and how rivers overflow their banks. What I do see in the vid is algae.
Lets not forget that our fish, inverts and fish food are putting things into the water. Also some folks add ferts for their plants. RO is not removing any of these things.
As for how long fish might live in tanks compared to in the wild is a bit difficult to access. in our tanks we can feed quality nutrician, we can successfully treat fish for a lot of things which would likely kill them in the wild. And then we ccan choose the inhabitants of our tanks and most uf us choose not to stock those fish likely to eat our other stock. And if we do decent maintenance etc. almost any species of fishthe fish should have a longer average lifespan in a healthy tank than it will in the wild. However, the knowledge to choose the right foods, to prevent most diseases and poor conditions are up to us.
How long a species may live in the wild may not even be known. We may not even be aware of that number when it is known. For most of us we have no idea if the fish we keep are living longer than they would in the wild. The one thing with which we must contend is the quality of the fish we acquire. For the most part we rely on sources of fish whose history we will never know.
