MH question.

[greenmaji]

How far would a MH bulb have to be up off the tank to cover 4 foot?

I double checked my center brace in my tank.. its glass with a little strip of plastic siliconed to the top of it to use the glass hinged hoods.. The plastic strip can be removed without much issue..

That is if a glass center brace isnt a problem.. wich Im assuming it isnt..

 

[greenmaji]

I was pricing MH and thought it would be cheaper to get a single 400watt rather then 2-175watt lamps for my 75 gallon.. it could be done for less then $150 depending on the bulb I chose to get..

 

[greenmaji]

Can a single MH even cover 4 feet of tank? :?

 

[mykpoz]

possibly... but i wouldnt count on it...

i was personally looking at 2x250 mh's for my 75g

 

[ccCapt]

You will get about a 2 foot square coverage area from 1 mh bulb. If you center it on a 4 foot tank both ends will be somewhat dark.

 

[MT79]

^^ I agree- 3 ft is really pushing a single MH, 4 ft would be impossible.

 

[fishfreek]

One bulb will not do a 4' tank unless you would be willing to accept the two sides to be in near total shadow and the middle to be insanly intense with light.

For 4' long tanks you should spec two MH bulbs both mounted about 1' in from the sides. This will split the difference on the center brace and any shadows that the brace might cast will be negated by the opposing bulb. A single bulb setup over the brace would also cast a shadow into the tank if the brace is not totally transparent.

Unless you was going to go for a full SPS tank you can get by with 175W mH bulbs over the 75. When doing MH you should match the ballast wattage with the bulb wattage. I like XM brand bulbs.

 

[Hara]

I notice you have an oceanic tank, if the warranty is an issue, you do NOT want to remove the center brace..it will violate the warranty.

 

[fishfreek]

In addition to compromisting the integrety of the tank. The brace would not be there if it was not needed for the better of the tank.

 

[greenmaji]

its not a brace.. *edit* acutuall numbers posted next.. I was guessing*edit* the actuall brace is a very thick sheet of glass over about 5/8" thick.. and about 6 inches wide.. the plastic is just a little strip glued on top of the center brace to it to accept standard double glass hoods.. (the plastic isnt even physicly connected to the front and back braces.. theres about a 1/16" gap).. its not helping integrity at all from what I can tell.. do I need to post a pic of this? it is strange that they put the plastic there IMO.
and the tank is actually very old.. not quite out of warntee I doubt .. I think they waranteed it for 20-25 years 8O, but Im not the original owner..

Ok.. the answer to the MH question is that 4' is really a streach.. but.. now that Ive noticed that this little strip of plastic is just there for mecanicly seperating dual glass hoods.. would it be benificial for me to remove it if I decided to go with VHO or other floresnt lighting? Or would the plastic strip not really matter in that case.. Im guessing it wouldnt.. ie leave it alone..

 

[greenmaji]

Ok.. I was guessing.. I got out the tape measure and measured it just now..
The center brace is 10 inches wide.. and its 3/8 inch thick glass.. the plastic strip is 1/32 of an inch gapped from the front and back plastic (just glued to the glass center brace)

 

[fishfreek]

If its just a divider than i suppose if you wanted you could remove it but it wont cause an issue with VHO or PC bulbs as they provide light over their entire lengh and thus will automaticly cancel out any shadow effect cast by the plastic part.

 

[Phyl]

In the case of a strip light (VHO/CF) that isn't a "single point of light" light like a MH the brace isn't an issue (nor is the little strip thingie that goes through). I had a current dual satellite over my 120 and it was fine. I'm now running 2x250 over my 120 that's 4x2x2. I wouldn't go with any less than a 250 over the 24" depth. Sanjay Joshi has some intersting spectral analysis using various bulbs and ballasts (and combinations) that I'd look to before I bought a MH setup ever again. It is interesting to see how the better bulb/ballast combos in 175 can outperform the poorer 250 bulb/ballast combos (same taking the jump from 250 to 400) so you may be better of with a really good pair of 175s then with the single 250/400.

 

[greenmaji]

Phyl.. do you have a link to the Sanjay Joshi analysis results? Or was it in print?
btw. thanks for the input so far everyone..

 

[MT79]

.. do you have a link to the Sanjay Joshi analysis results?

http://www.cnidarianreef.com/ The link is to the right.