Green Neon Tetras In Hiding

[r.w.girard]

I have a heavily planted 20 gallon long fish tank [30x12x12] with low-lighting and an Eheim 2217 with the output running the length of the tank.  The tank houses a school of some 23 Parachierodon simulans, 2 Otocinculus sp., a breeding pair of Mikrogeophagus altispinosa.  The water is somewhat acidic, in the mid to lower 6s, I think, because of the mopani in the tank. The water is harder, but the fish show pretty good color, although not much red, and eat well.  All the same, they are always hiding and never use the full length of the tank, always remaining the the left half of the tank.  I was wondering how I might coax them out and get them to swim around a bit.  I tried rescaping the tank about a month ago, mainly for the benefit of the rams, but that didn't change anything. So is there something that I am missing? Do they need more "open" space? Less flow?  With such a large group and no boisterous fish in the tank, it is hard for me to understand their lack of temerity.  I could upgrade to a taller 29 gallon tank [30x12x18] in the next few months but I don't know how much that will change things for the Green Neon Tetras as they tend to inhabit the bottom portion of the tank.
 
Any ideas would be appreciated.

 

[VickyChaiTea]

How low is low lighting? Maybe you can add some floating plants for top cover. That's all I can think of, unless the fish are new to the tank.

 

[r.w.girard]

Thanks for the answer.  Half of them been in the tank over a year now, the rest, a year and half.  The lighting is an old [over a year] 24" 18w T8 bulb. So not strong at all.  And the surface is largely covered by overgrowing sagittaria.  So I doubt its that...