Metal Hallide VS T5 HO

I sadly only have a minute to respond, but I will be back later to fill in the blanks, but for now I will just cover some basics and give a little food for thought.

Firstly know that WPG is only to be used as a guideline. The intensity of the lighting, depth of the tank (well technically how deep the coral is), shape of tank, etc all play a part.

Here is a kind of extreme example... say you have a 1000 gallon tank with a 250W metal halide light right over the middle, and a 20 gallon with 80W of normal flour lighting. The 1000G would have a WPG rating of 0.25 and the 20G would have 4 WPG (thats 16X the WPG in the 20 gallon). If you had a coral near the top directly under the 250W halide in the 1000G you would see much better growth even though the WPG number is so much lower than the 20G tank. The only thing that really matters is how deep the coral is (how much water the light must pass through) and what type of light you are using, it doesn't matter if there is another 500G of water in the tank or only 5G. The only real way water volume plays a part in relation to coral and light is in keeping the temperature more stable...

Metal Halide is the most intense of the types of lighting. That does NOT mean that it produces the most light for corals to use, just that the light will penetrate the water better. Less intense lights may appear bright but dont have the "punch" to really support many corals unless they are up near the top of the tank. Metal Halides have more "punch" than other light systems. T5 lighting is the most efficient of the flourescents and works well for most corals. Im sure that there are many people that have kept "halide only" corals under T5s. Overall it will be up to you and what you want to do more than anything else. Halides definately help and work great, some people just dont want to take the step up to them. The halides also give off all their light from that one point which gives of a shimmer effect that you can see in the tank (which many people like), the T5s give off their light over the whole length of the bulb and doesnt give off the shimmer that halides do.

I know this doesn't really answer your questions, but I hope this helps at least a little bit. If anything is confusing or worded badly let me know, I tend to do that when I haven't slept... Also any thoughts on what you plan on doing with your tank/corals would help us to suggest different ways to go. Anything you definately want to keep, etc, etc...?

Rick

Here's a very general breakdown of T5-HO versus MH.

Initial Cost: For top-end T5 systems like Teklights, Ice Cap and Aquamedics with individual reflectors etc. you'll spend more than a comparable MH system. Of course there are cheapy T5 systems like Finnex, but these don't take full advantage of the T5 technology and I don't think they can be comparable. Winner: MH

Running Cost: Comparable T5-HO systems use less wattage than MHs. Europeans use T5's more because of the higher energy costs over there. A 6x54W T5-HO is roughly equivalent in PAR (IME) to a 2x250W MH system (both cover a ~4'x2' area). You do the math. As far as bulbs are concerned, T5 bulbs last longer than PCs (up to 18 months). You should also replace MH bulbs in about the same period. You'll have more bulbs to replace with T5s, but they're cheaper than MH bulbs. Here in Canada, an 54W ATI T5 bulb goes for around $30-40 whereas a 250W Ushio MH bulb (mogul or HQI) goes for around $80. As well, many MH users also supplement with additional T5/VHO/PC supplementation adding to cost. Winner: T5

Flexibility: There are many types MH bulbs available, but you're limited to ONE bulb at a time (unless you've supplemented as mentioned). T5s are easier to mix/match and fine tune colour temperature with multiple bulbs which can be changed out wholesale or one at a time. You'll also need supplementation if you want a dawn/dusk effect with MH. On the other hand, it's easier to "hide" low light corals with MH since it creates shadows unlike T5 which puts down the same amount to light across the entire length of a tank. Winner: T5

Heat/Safety: T5s produce far less heat the MH. A MH bulb will burn skin, a T5 bulb feels like any other fluorescent - hot, but not burning. You'll need fewer fans with T5 and will have less evaporation. MHs also require big bulky ballasts. A reason I went with T5s is because there's a 3 year-old poking around my living room (where the tank is) constantly. Winner: T5

Looks: Entirely subjective, but you CANNOT get pretty shimmer lines with T5 since it's not a single point light source like MH (or the sun for that matter). Some people just don't think that T5 lit tanks "look" like a reef. Winner: MH

In the end it's up to you. MH is tried and true, but T5 is very intriguing.

BTW, why do you think you need 400W MH for a 100 gallon tank??? What do you plan on keeping in there? Most people with tanks less than 30 inches deep (like a standard 100 gallon) keep the most light demanding corals and clams with 250W system. You can have TOO much light especially if you plan on keeping a mixed reef.

I use 3 175s on my 135 *shrug*

I dont think im gonna do any acropora or any of the corals in that family because i dont think im ready for the demand that they take yet

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They can be just as complicated as

BTA's(hopefully rose) and clams

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is 800w MH too much for a 20" deep tank?

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Very well could be, are you talking 2-400w? And how close to the water? UV deflectors of some sort? Do you need two 400? No, not if your tank is 100 gal. How long is your tank? 4 foot? If so, 2-250s or two 175s with supplimental light will work for a 20" deep, like flourescents with actinics.

We usually look for 5-6 watts per gallon on MH, that is rule of thumb, as 8 watts per is heavy lighting. Mine is 24" deep with 3 175s and 4 40w flourescents for suppliment and I have no problem housing my SPS.

For all the animals your looking at, only the Clams would require the MH lighting in an amount of 175-250 watts per 2 square feet, I personally think you could cook anything with 400w over a 20" deep, but thats me.

Hope this helps, try reading some of wetweb threads on lighting requirements.

Acro's are regarded over where i live as beginners corals, many of the newer people the the hobby are able to keep acropora's alive, the only reason i can think of why your's died is warfare from the anemone, or maybe not enough current? Also they are pretty cheap over here around $10 a frag and $20-30 for a big one, and that is australian dollars, also how much water movement did you have?

All i know is that for most sps and reef aquariums, aquariasts aim for around 30 to 60 x turnover an hour, so that is probably what happened.