Pure Ro

It depends on just how good your Ro unit is I guess. Different RO membranes take out varying solutes. A good membrane will reduce the water to almost distilled water content, but will never truly remove all solutes. You can use Pure RO on discus - and discus only (plus cardinal tetras etc), but I would strongly recommend the addition of a solute/electrolyte replacement of some kind. We use a SEACHEM brand discus salts/solutes. Works really well with RO water supply.
To say that pure RO works on fishes is not true. To start with, you have an organism that exchanges electroytes through the gills. Its whole life depends on being able to stop salt/solutes from escaping from its body. Discus are about the best at doing this in a pure environment.

Pure (and really good RO) water should be similar to distilled water. The fish spend too much energy forcefully trying to exchange osmotic imbalances in that kind of water. I would like to look at your fishes gills under a microscope, because I believe gill damage would be occurring under pure RO water. They would be working overtime!!

Heckel discus live in a 'soup' in the wild that is very high in Humic acid content. This is from surface soil/humus run-off. The pH is low because of this. The total dissolved solute content is not low however. This is exactly what RO water removes.

Do an internet search and see just how 'toxic' RO water is without the addition of relative solutes is. Another journal you can visit is -journal of aquatic animal health. The proof is out there - Pure RO will kill

Squid

PS. I can find info on this subject if anyone is wanting it

yes please on the info

any chnace of an accurate breakdown of the dissolved mineral content of native waters

andrew

ps i use straight r/o with peat to acidify for many of my apsito species

Andrew - I'm out of town until mid Jun. I'll try and find some info on gill changes in RO for you when I return

Squid

bump
what happened with those references


i totally agree that pure water, with absolutely nothing dissolved in it is not appropriate for fish
and i also very much doubt that any fish tank could be like that no matter how hard we tried to achieve it

r/o units are maybe 95-98% effective when working at their optimum... so there is always something left in the water
natural acids like humins and tannins etc are dissolved particles and must have some osmotic effect

black water habitats of apistogramma are recorded as < 12us/cm for conducitivty, calcium and magnesiun levels < 1mg/l and pH 4 to 5

other habitats are suggested as having conductivity upto 800 us , unfortunately i cant find any specifics on total dissolved solids