Yeah the 8-10 KH was what the LFS was recommending as a generic number - I believe I will target around 5 if that will be enough to keep my PH stable.
While I recognize excel isn't as good as pressurized CO2, I thought my light would be sufficient. Based on the CFL research Hoppy did here: Lighting an Aquarium with PAR instead of Watts
take a look at this chart:
he shows around 35 PAR at 24" for a 15 watt CFL mounted vertically. Now mine are horizontal and if you look here:
PAR Data-Spiral Power Saver Bulbs, lighting question
you can see that horizontal is less efficient - maybe by as much as 50%. So if I am only getting 35/2 or 17 PAR/light x4 I am 68PAR - and anything over 50 Hoppy classifies as high and I need to worry about CO2/ferts.
Don't get me wrong, I am totally new at planted tanks/lights/ferts all my experience was just fish and plastic plants before, so if you can help me understand please do. I just need to be able to understand to accept it