The effects of ferts on TDS - Osmotic shock?

[JosVermeulen]

I've been wondering something and I've talked about it with several people, but I couldn't find any scientific paper on the subject. Wouldn't dosing ferts combined with water changes cause changes in TDS and hence cause osmotic shock(s) which are harmful to fish?

 

[Hugo_Abreu]

For what I know, only harms the fish if the change in TDS is very big. And in some species, only in one way. For example, some fish from small streams of water in South America (some Apistogramma, for example) are adapted to fast changes from hard to very soft water. Why? Because when the rainy season starts, the rain water is so much (and has 0 TDS and a pH of about 5) that the stream water goes from (imagine) 100 ppm to 50ppm in minutes. Hope it was clear and helpful. If I'm saying something wrong, please correct me.
But I suppose it could cause that osmotic shock...