I bought some Cabomba a couple of weeks ago and it seemed to do OK at first,
but has been losing needles lately. I know the water was too alkaline for
it, but my CO2 regulator was delayed. I have the CO2 running now and the PH
is down to 7.5ish for now. I plan to go to 7, once I get a PH controller.
The soil is not the greatest either, plain aquarium gravel (clown puke) with
quite a bit of natural sediment. Everything else is OK, light, Iron, N-P-K,
etc.

So do you think the PH is the main issue? It does seem to look a little
better tonight, but that's somewhat subjective.