i actually heard the sudden death of most payara comes from living in harder water than they do in the wild and it takes around the same time to die from it so thats why everybody's payara die around the same duration of owning them.
A 7" pleco I have had forever and a small piranha that has been in the sump tank for months. I had no room for him and was trying to find it a home. That is it.
I grow a bunch of hornwort in a portion of my homemade sump. I always have plants in the sump to consume nitrates and they usually stay low especially with only a few fish stocking it. My one tank never shows nitrates because of all the plants. I normally do 2 20% changes a week with chlorine remover premixing the water. I do not have an RO unit though.