I'm glad you chimed in A.grandis!
Since I'm removing a couple rows of T5 and my LED 50s, I was going to jump straight to 6 hours of halides. (especially since they're only 175 watt). I'll start with 3 hours per your suggestion.
No Problem!
In reality you don't really need supplementation at all using halides, if they are used with the proper fixture for the tank. Most public aquariums and reefers don't use supplementation at all, as an example. I've never had ReefBrites, so I don't know how they behave in regards to distribution, but I would think it would be a great fixture for what it is, as many say. Just keep in mind that with T5s, halides work as the "sun" and T5s work as an "overcast day light". When you put them together you will have results similar to the light from blue skies and the sun over the reef altogether. That is the concept of having them as a combo. The T5s would "fill up the gaps", if needed. Halides are a point source, and the T5s cover the system as a sheet of light. Visually the halides will just overcome any other supplementation, but the T5s do play some into the combo IME. LEDs are another point source, like halides, but people use them for the "blues". I do not see any LED as a substitution for T5s. They can "look like", I guess.
After testing for couple of years, using halides and T5 together is what will give me the best results for what I want. I personally don't care for the "blues" from LEDs.
There is nothing wrong in using all 3 over a system, but just keep in mind that what halides will offer to the corals is enough for them to behave most like they behave in the ocean. Halides are pretty strong in spectrum and intensity alone, not to mention the unique shimmer and UV/IR, which in my point of view contribute greatly to the health of the corals and do make a difference visually.
If you want to use all 3 types of light you need to make sure they don't overkill, which is very easy to attain with halides alone!! That said, when using halides with T5s, you will already need to pay attention to prevent excess of light throughout the photoperiod. When you add the LEDs on top of that it's even worse.
My advice?
Use the halides as the main source. max of 4 - 6 hours max.
T5s can be used for up to 9 hours max with halides without LEDs, and that would be enough light. In truth you don't really need to use the t5s while halides are on, if you don't want. I do.
The LEDs for sunrise/sunset hours, 2 hrs a day alone (1 hr. in the morning and 1 hr. in the evening) would be more than enough if you use the T5s and halides already! With you use the LEDs you can use the T5s for 7 hours, instead 9 hours.
I'm not sure why you want to use all 3 types, but you can actually choose between T5s or LEDs for supplementation and still have plenty light. You must have plenty room above the tank to be able to fit everything there. I know the ReefBrite halide fixture allows that type of set up and that is an advantage in your case.
Congratulations! Your system will explode with life! Let us know how you like the ReefBrites! Go slow!!
