Well, the problem solved itself. They, as well as 3 corys are all dead now.
Have no idea wat I did wrong, but it makes me sad, to see even some small lives wasted.
Water is clear, ph shows at 6. Old fish ( used to swimming in poison ?) are still thriving. Although two of my tiger barbs have disappeared.
Nowhere to be seen, not even behind or next to tank , just in case they jumped through the small cracks between the tank and the cover.
Ié had aquariums for many moons, wbut this is the first (20 gallon) tank I have such trouble with.
Perhaps I should take the others out, transfer them into an old 10 gallon, with the water they are used to. And than make a clean start (again) with the 20 gal
. Get new gravel or cook the old one, to kill all bacteria.
I am very ill, and old, and have not much energy though. perhaps i should let them jus live out their little lives, and call it quits.
Thanks for the forum and all the good advice I have picked up.