"Graham Broadbridge" wrote
Anyone have any suggestions about how I may improve the water chemistry to
get the plants in action again

How old are your lights?
I had some issues a few weeks back with slower growth & BGA.
I replaced a tube that was only 9 months old & now all is OK.

--
Graham Ramsay
Blairgowrie (UK)
www.ibrox.freeserve.co.uk/aquarium.htm