t5 yes no...

[Stones]

I recently saw my first SPS/mixed reef tank lit soley by T5's and I was seriously impressed. The tank was lit by an 8 x 54 watt TEK fixture and all corals had amazing colours. Growth rates in his tank seemed to be on par with my tank however I too am using 2 x 250 watt MH as you are, but the T5 tank had much better colour. After seeing that setup, there is not a doubt in my mind that you can have a beautiful sps reef under pure T5 lighting.

[kwirky]

Both lighting systems give great growth. If you already have a combo system though I think it'd be cheaper to just replace the one ballast than rather convert the whole system.

14k MH with fiji purple T5 is almost exactly the same as running 50/50 T5 with new generation and fiji purple. Growth is pretty similar I find, between the tank at the store and my tank at home. (T5 tek at the store, 250W DE electronic MH at home). Colour's better at the store but I'm planning an upgrade to a combo T5/MH system anyways.

[sphelps]

I think it depends a lot on the tank Dimensions, if you can fit a good amount of T5s over the tank then it`s good choice for lighting. I went all T5s but ended up going back to both T5s and MH, It just lit my tank better and liked the look. All T5s actually produced a lot of shadows while using some MH as well eliminated most of them.