T5 actinic are 420nm violet and aren't that great, they look good at first but dwindle quickly, they are very low PAR and don't compare to blue plus or blue bulbs in the 460nm wavelength that also make your coral fluoresce but will also make them grow unlike T5 actinic.
T5 actinics do t compare to VHO or PC/CF Actinics, the higher wattage really makes actinics a lot better than the low wattage T5 counterpart unfortunately.
I suggest a combo of T5 blue plus & purple plus I stead of T5 actinics unless you are going strictly for actinic dawn/dusk combo with 2 bulbs.
I say try 1 t5 actinic at first but would not buy Hagen/fluval bulbs. Try ATI, GIESSEMAN, & KZ.
I know all about Hagen/fluval bulbs...life GLO, power GLO, flora GLO, etc...
I avtually don't mind the 18'000k power GLO as a purple bulb replacement, you can get a GE6500 for way cheaper than the lifeGLO II bulbs and the ge6500 is better IMO.