Help!!Confused about MH

newbiereefer · Jan 31, 2005

I have a 90 gal standard acrylic tank. Have been up and running for about 4 months. Everything I have was from a divorce liquidation sale

(the best and cheapest way).
I want to purchase MH-pc light hood but I am very confused on which is better and safer. I am thinking about a coral life 48 inch that has 2x 150 10k MH and 2x96 watt pc, which gives 492 watts of lighting. Or should I get 2X250 10k MH with 4 pc. My questions are as follows
1.Is 492 watts enough to have SPS and clams?
2. Can I put this in a custom hood, if so, what should be the min distance from top of tank. Will I run in to temp problems?
3. This unit has the MH center in the hood. Does it matter if they are in the center or should the be located more to the edge to allow for maxium light thru the tank.
4. Has any body ever heard of MH cracking acrylic? Was told it could happen.
Any suggestions would be great.
JIM

The R/C Man · Jan 31, 2005

Welcome to RF!!!

Well first thing is the watts, 500 watts of PC or VHO is not the same as 500 watts MH. MH is a pin point type of lighting and will penetrate the water much deeper. I believe the 150's won't be enough. Depending on the depth of your tank I would say use the 250's. I have a 250W 10K on my 25 gallon. It is supplimented with two 65w PC actinics. If you are looking to save a few bucks use 20K bulbs. You will not need actinics for supplimental lighting.

Depending on you mechanical ability you can retrofit anything...

Personally I like the mogal bulbs with a nice reflector. You can mount them in a variety of ways to include hanging them from your ceiling. If one bulb gets splashed and breaks there will be minimal glass in your tank. The double ended bulbs require a uv resistant glass between them and your tank. If it gets wet and breaks there will be large amounts of glass the tank and the unbroken bulb will "cook" your corals....

Just some food for thought...

plack · Jan 31, 2005

I've seen some say 7-8 watts per gallon is a kind of minimum for spc if you plan on soft coral's that's very different they don't need as much light it depends on what and how much you plan on getting the depth of the tank and distance from the light to the coral etc i have 440 watts of vho on my 55 gallon with just a few of the less demanding sps (montiporas)

BCT182 · Feb 1, 2005

My understanding is, if you have halides and your tank isn't super tall, you can pretty much do anything. WPG isn't a good wy to determine what you can and cannot do with so many variations. Kalvin, tank depth and so on. I think, you could probably have 5-6 "WPG" and still do quite a bit, if your tanks less than 1 1/2 feet deep? Just my opinion.

Maxx · Feb 1, 2005

A rough guideline for tank depth and MH wattage selection is:

18 inches or less (in tank depth) 175 watt MH's
19-24 inches 250 watt MH's - mogul/screw in base
24-30 inches 250 watt DE bulbs or 400 watt mogul/screw in base
30 + inches 400 watt DE's or 1000 watt mogul's

I say rough because this doesnt take into account bulb selection or reflector selection whihc has ALOT to do with the intensity of the light reaching the corals in the tank. Something else to keep in mind is the distance the lights are suspended over the tank.....higher means less intensity reaches the bottom of the tank.
The reason the DE bulbs are reccomended for deeper tanks isnt because they produce more intense light, its because they have better reflectors that direct more light back into the tank. The only exception to that particular thought is the Diamond Lumenarc reflectors....they are very, very good at reflecting light from mogul lamps....they're just very hard to find, and they are very large.

here is a link to more info on MH's than you could ever want to know...
Sanjay's Reef Lighting Page

HTH,
Nick

Ed Hahn · Feb 1, 2005

My oppinion is if you go with two 250 MH in your ninety, you will not regret it. You should be able to grow most if not all SPS and clams. I am up grading due to watching friends growth rates with 400's watt MHs.
I hope this helps,
Ed