I think shortening the lighting would help with the acclimation. Double the light can induce "light stress" causing corals to close up, slime, and LPS
corals to start having tissue recession. I would have your actinic lights come on 2 hours before your daylight, then run your daylight for 3 hours, and then have the actinic lights run another hour before having the fixture shut off totally.
Then a week later I would have your actinics run for one hour, your daylights run for five hours, then your actinics run another hour before the light goes out.
After a week of that have your actinics run for one hour, your daylights go for 6-7 hours, and your actinics an hour before it goes out.
Finally run your actinics for an hour, daylight kick on for 9 hours, actincs two hours, unit off and that works well as a final light schedule.
As for Maxima clams under T-5's - Ive seen Maxima - Crocea and Dersea clams all thriving under T-5 lighting. For fast growth speeds and ease of care I would recommend a Dersea if this is the first clam you are keeping.