Advantages of T5 over VHO is the light output per watt. The bulbs are only 5/8" wide so you could cram more into the same space. The T5s are more efficient than VHO and the reflectors are computer designed to actually send 300% more light toward the tank than without a reflector or if using a flat reflector.
I had originally planned to use two 250MH with a 4' T5 on each side for supplementation so I could just have the T5 on for most of the day and then run the MH 4-6 hrs to give the corals the light they needed. When I moved everything over to the 75g tanks I didn't have my MH bulbs yet so I just ran 2 T5s over each 75g. I had an 8" squamosa clam and a 4" maxima. The clams were doing great and the corals were looking good too. When I got my bulbs I had some ballast troubles too and decided to just get the IceCap SLR reflectors for the 4 bulbs I had.
When I was at the CORA frag swap I won another Ice Cap 660 and decided it was time to double the light. Everything was growing well and I had quite a few SPS growing. It had been about 8 months with just two bulbs over each 75g.
I added 2 more T5s to each 75g tank for a total of 4x 48" T5 over each 75g but I could run 2 at a time since there were 2 ballasts now.
Recently I squeezed everything together and added one more T5 over each 75 for a total of 5 bulbs so I have them set up on my controller to have 1 bulb on, then 2, then 3, then 4, then all 5, then go back down to 1 and off. I had some corals bleach slightly just from adding the 5th bulb but they are adjusting now.
The 92g corner tank has 4x 36" bulbs with SLR reflectors and 2x 24" bulbs with SLRs. I have the 2x 24" wired to the same ballast as the new 5th bulbs on the 75s so I can light the two 24" bulbs then have the four 36" then all 6 bulbs and work back down to just moonlights again.
I have two 4" derasa clams and one 8"+ squamosa in the 75g and two 4-5" derasa clams and one 12-14" derasa clam in the 92g. The largest one is on the sandbed 24" below the 36" T5s and looking great.
Overall I prefer the ease of changing colors by just replacing one $22 bulb and the whole tank looks different.
I have a 6500K GE bulb in there for some growth but it washes out all the blue. They are very yellow bulbs. I replace the bulbs about every 18 months. I usually buy 2 bulbs at a time and replace one over each tank about every 4 months so it takes 16-18 months to replace all 4 bulbs and I never really have to dish out huge chunks of change like replacing 4 MH bulbs at once every 8 months to a year at $70 each.
I will be having a tank viewing night and we will be making up some frozen coral/fish food on the 19th of July so if you can make it you could check out the lighting situation in just a couple weeks.
There is a HUGE thread about T5 PAR ratings and many suggestions about bulb mixtures that you can check out
HERE
It has split many times but it is still active.
Also worth mentioning is the fact that the T5 bulbs that are 54w on a regular ballast are overdriven to about 85w each on an IceCap660. So I am running about 425w over each 75g tank and roughly 350w over the 92g tank. It is not much cheaper on the electric bill but I have less heat issues and cheaper bulb replacement at each hit. If I had to replace them all it would probably cost about the same as MH at $110 per tank.
One nice thing about the T5 is that you can have a much lower profile canopy since you can have the bulbs 2" or so off the surface instead of 8" that is recommended for MH bulbs.
As far as VHO compared to T5, You would be shocked to see the difference between them. I think CrazySeany changed his VHO to T5 and was amazed. If you are about to buy bulbs try this experiment. Just change out one bulb to T5 endcaps and a bulb. ($15 for endcaps/standoffs and $22 for a bulb)
Compare that one bulb to the other 3 VHOs. You can mix them on an IceCap660 ballast and could change over bulb by bulb as you can afford it.
Funny thing is that when I started my first reef tank I had a 400w 20K MH over a 29g tank LOL. Now I am about as far from that as can be.
Any more questions feel free to ask.
Hope that helps.
-- Kevin
