Thanks everyone for the ideas...
You have me thinking about light... it's the great unknown here... I am using par38 LEDs and I have no frame of reference for PAR values as they're not very popular... I wish I had a meter to see what im actually dealing with...
Assuming the co2 and flow/distribution is consistent and my fertilizers are adequate or close to it, the limiting factor could be light... intensity or shading or photoperiod... if I had a meter I could rule out intensity... I don't think I have a shading issue besides the maidenhair fern for one area as I designed the riparium section to be way behind the submersed growth... so maybe it's photoperiod...
I started the tank as a drystart method in Nov or Dec of 2016 at 100% brightness for 12hrs and once filled in Jan 2017 I think I lowered the intensity to 75% for 6hrs and ramped that up to 7hrs after a month... I did not experience much in the way of algae until the summer and that was black fuzz on the carpet plants that stopped growing and synedra after that and was probably associated with high organics... after battling that for a longtime, I lowered the intensity to 65% in Feb 2018 where's it stayed until the summer where I had a greenwater or bacterial bloom at which point I lowered the intensity to 55% for 6hrs with a 30min noon at 75%... some synedra algae continued, but since cleaning the the poret filter and and sucking out all the mulm in the sump, all that has disappeared... there's only a tiny bit of bba here and there but nothing to worry about... Last month I increased the lights to 60% because I didn't like the spectrum at 55%... it seemed too blue and I'm not sure why...
And that's where we sit now...
What does all this mean? I have no idea what I'm doing with the lights... turn up the intensity? I'm afraid of an algae farm that will have to battle... longer photoperiod?
Obviously the emersed plants grow... but really the only stems that do well are hygrophila polysperma and now heterantha zosterfolia... the hygrophila angustifolia isn't doing well and as mentioned the dwarf sag is struggling and all other carpet plants died out except cryptocoryne parva and nevilii... Ludwigia repens disintegrated and the Lysimachia nummularia 'Aurea' isn't far behind... Cryptocoryne wendtii and lutea grow well on the sides and of course anubias do well...
I know I'm nitpicking at this point and overall I love the overall look of this tank, but I tend to overanalyze in the cold depths of winter.. . Pretty soon it will be spring outside and I will neglect the tank yet again...