175wMh is fine for your 30gal tank IMO.I would not use a 20k bulb with a 175wMH,they are very dim compared to a decent 10k bulb.If it were me,I'd add a pair of T5 flourescents to supplement your 175MH.A 2x39w T5 retro can be bought for $115.As for flourescent actinic bulbs,i prefer a T5blue(ATI blue,CV actinic) or a PC blue.The wavelength(450-460nm) of those bulbs really bring out some wicked colors IME