T5's dont penetrate very well in deep tanks so to make up for the lack up PAR you would just run your bulbs longer. When there is an excess of PAR usually from MH or T5 in shallow tanks there can actually be a negative effect on growth and color from running your lights to long. 12hrs is usually the longest ideal time to run them, some people have great results with 8 or less hours. I run my T5's for 12hrs with my Ati blue plus' and 10hrs with my full lights on. When i replace my bulbs next week i will lower this to 10hrs blue plus and 8hrs full lights for the first few weeks to help acclimate the corals and then slowly bring it back to the old regime. You can always plus with the time a bit you might be supprised that lowering the light time might give you better results. I have found in my current tank the 10-12hrs works best for growth.
My lighting schedule looks like this in my 50g with 6 t5's
10am - 9:30 pm 2x ati blue plus
11am - 8:00 pm 3x ati blue plus 2x ati aqua blue 1x actinic white
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