I remembered we have similar water from when I bought those nice shrimp from you a few months ago. They're in the actual Dutch btw. I threw 10 more fire reds from a different source in there to tighten up the bloodline...done had a few babies
I use straight tap with KH ~5, these are in sand but it grows about the same in soil. It can be a finicky plant, quick to stunt if it doesnt like something. On any given day I probably have 1 out of 9-10 that is stunted. Thats about as good as I can grow it and I just pinch those off and let new side branches come in. Dont show them in pics and dont sell them, lol. Thats how I solve it!
Now if yours are doing worse, say 50% or more stunted...idk. Probably needs a little more something. In my set ups it tends to balk at too little, not too much
Either way its not your KH or inert sub. Clean tank and good co2, Im sure you have that too. Light I run about 120-130 uMol at the sub, no idea what it would do under more or less