The thread has been very interesting to read. Thanks for all the useful information.
I have been struggling with plants for a few years and have stupidly proceeded by trial and error rather that stuying the forum in more detail. This is the limited knowlenge I have gleaned from my own experience:
Most plants seem to need sufficient CO2 in the water, regardless of how 'good' the substrate is. Cryptos seem to be an execption in that they appear to thrive in my tanks with low CO2. They seem to feed heavy of the substrate (massive roots) - but didn't seem to grow as well with undergravel filters on.
If you use a CO2 system, make sure it works on a timeswitch with the lights.
Lights - my growlux (type) tubes are less effective after about a year. I don't wait for them to fail before replacing them now.
From observation, I'm convinced that algae can utilse light for a longer period each day that my plants. I am experimenting with the idea that it is betterto increase the intensity rather than extend the time period beyond 10hrs/day.
I must try to get a better knowledge in these areas and have wasted much time but I hope you find my experience useful.