Love your hardscape! I have used echinodorus tenellus before and once they start growing... they can get unruly and overtake the rest of the plants. I think echinodorus tenellus will fit will in a jungle scape.
Please put your hobby grade test kit in the bin or if you insist using it, ignore the results....Son did a few tests (API Master)
Bit shocked at the hardness, will retest tomorrow. It is what it is.