Hi Chuck,
Thanks for your input.
My setup is fairly simple. I don't currently have a planted tank per se - it
is WIP.
Current setup:
- 25 gallons
- 5 plants
- 18 watts light (don't laugh please)
- no CO2
- 1 adult , 2 juvenile platies
- 5 neon tetras
- 2 pieces of mopani wood
- 300gph rated power filter
- 100W heater

gH = 3
kH = 3
Temp = 79-80 oF
pH = 7.8 - 7.2 (over a week say)

1-2 x 25% Water changes weekly
Tap water
gH = 3
kH = 2-4
pH = 8.0-8.2

Symptoms - dead neon tetras