Yeah , i agree with limbssg and drattg.
Check yur parameters...frankly speaking i dont think the UV is that important a piece of equiptment la.
And with 5 - 6 watts... i think not much of a diff leh...
SHould pump yur money into yur filters and skimmers instead.
If u havent had any water testing kits, i strongly suggest that u get AT LEAST an ammonia tester, a PH tester and an NO3 tester. These few are by far to me the most basic lah.
AND ALSO SG (specific gravity... saltiness... hee)
How about the rest of yur livestocks?
If its only the angels, then it might be the LFS that u get them from.
My 2cents.