Apistogramma,Mikrogeophagus Ramireiz (sp),otocinclus, are a few that do better,longer, in my expieriences with lower tds .
I did not say TDS kill's fish ,only that some species do better with lower level's.
I did not say fertz was issue, but only contributer to TDS as is everything organic/inorganic we add to the tank.
Some may wish to google/bing,"effect's of total dissolved solid's on aquatic organisim's" (American journal of enviornmental science's) for more understanding.
All I said ,and still believe,is some wild caught species do better with lower TDS .
Do you dispute this?
Otto cats most certainly.
Apistos often come in in batches, even with low KH water and peat, many importers and breeders lose the wild fish.
I agree they do better, but I'd argue that it's the KH that matters, not the TDS as much(but they will be related to some degree).
I'm not a specialist and most people that buy wild apistos are going to be specialist.
I stated you need a specific ppm. What is a high TDS? 100? 200? 300? 400 ppm?
What is a high level of ferts? Any idea? I'd suggest EI is the upper need for any aquarium pretty much.
How much above the tap's background does EI add to the TDS?
Test it and see. I'm not going to answer this because you or someone else should do this, then they will know the TDS contribution from dosing.
Perhaps it's just the KH and not the Ca and Mg levels. I've found this to be the case with Discus, they colored up and did excellent with high GH additions.
Then several breeders here in the SF Bay area USA tried it after seeing a few of the fish. They reported similar results. the KH wa slow, but they raised the GH(and thus the TDS).
I've breed 3 species of Apistos over the years, I have rams and a few others in client's tanks. These are not wild however.
Perhaps they are radically different than the Altums and Discus?
Could be. But maybe not.
If you have to use one of two genera of only wild caught specific fish that demand low KH water..........now you really are being specific, which is good, but then you lose the notion that's it's a generalized problem for fish keepers with adding ferts. It's only is a few very narrow specific cases and even those might be due to other issues than TDS.
Lots of possible issues.
You have to go down one by one and rule them out or see if you can. Sometimes you cannot, sometimes you honestly do not care, the advice works based on correlation and that's good enough for many hobbyists(I've done it as most of us have at some point). Maybe it's tannins vs none? I've seen this also. Can I say much about it? Same as you with the TDS. But I have to say it's correlation but I'm unwilling to test with fish as much as with Shrimp culls. Driftwood laden quarantine tanks always seemed to do best for me. These have higher TDS than the other tanks. I've brought in a lot of wild cardinals/Tetras over the years, the addition of GH seems to help, the tannins seems to help also. Been on both sides of this fence.
Still, the questions I pose are valid and informative questions, questions that would help aquarist later in the future to define what are the best management practices for livestock, plants etc.
Guessing does little to help further the knowledge base. Myths do outright damage. Good TDS reading ranges may help and give a nice base line so that others can compare and see if the results are similar.
Same with ferts, shrimp, other wild species, breeding, coloration etc. They have tannins testing kits, but few measure it. KH and GH test are easy, same with TDS/EC.
I suppose I should see about the tannins, I've always wondered about it.
After the fish have fattened up, done with quarantine and been doing well, then the TDS is adjusted up, is this an issue?
Might be transport, weakened state of the fish etc. While I have not brought it Apistos from the wild, I have brought in many fish from the same/similar locations.
TDS from ferts have not been correlative to poor health for me with any of the species I've had, Discus, catfish and all the way down small tetras.
I quarantine them however.
Then once fat and happy, then I add them to the client or my own tank.
My tap has a KH of 18-20 ppm, and rises to 35-37 ppm seasonally.
So it's pretty good.