Just an observation here - a few days ago I was trying out lighting to take some better pictures of my tank. I had the current 36w PC T5 tube on (15 UK gallons tank) which is housed more towards the rear of the hood. I then added an 11w tube to the front of the tank which evened up the brightness across the whole tank - I quickly noticed that fish colours were much improved, as an example the copper areas on my harlequins were much move vivid and looked really good. Initially I put this down to the different spectrum of light from the 11w tube, but I then did a bit of playing. It seems that the improved fish colour was actually down to the position of the tube - having light pretty much overhead gives an improved fish colour than having light towards the rear of the tank. Moving my PC T5 to the front of the tank had the same improved effect - however this lead to a significantly worse spread of light over the tank in general which is not good.
As a side effect I also noticed that within a few minutes of moving the light towards the front, my front plants (glosso, windelov fern, p.helferi) started to pearl, something they have not really done before despite having ~2.5wpg (using CO2 and EI aswell) - I guess this suggests that whilst I have a fair bit of light, the spread of it across the substrate is not very good which may further explain why I constantly get long thread algae amongst the plants that grow directly beneath the light, the light intensity from the PC T5 tube is pretty concentrated.
I am now debating moving to a two-tube setup, but it looks like I might have to take a drop in wpg to achieve this - I can't think there is a major problem going from a highly concentrated output from my 16" 36w PC T5 and one reflector to a much more spread output from two 18" 15w T8's and therefore two reflectors? I am limited in space within the hood (and don't want a luminaire) so can't go beyond 18-20" in tube length so two 15w 18" T8's on a double starter is likely the easiest option.
As a side effect I also noticed that within a few minutes of moving the light towards the front, my front plants (glosso, windelov fern, p.helferi) started to pearl, something they have not really done before despite having ~2.5wpg (using CO2 and EI aswell) - I guess this suggests that whilst I have a fair bit of light, the spread of it across the substrate is not very good which may further explain why I constantly get long thread algae amongst the plants that grow directly beneath the light, the light intensity from the PC T5 tube is pretty concentrated.
I am now debating moving to a two-tube setup, but it looks like I might have to take a drop in wpg to achieve this - I can't think there is a major problem going from a highly concentrated output from my 16" 36w PC T5 and one reflector to a much more spread output from two 18" 15w T8's and therefore two reflectors? I am limited in space within the hood (and don't want a luminaire) so can't go beyond 18-20" in tube length so two 15w 18" T8's on a double starter is likely the easiest option.
