MH light questions and Wattage

[hsiehqf]

Hi all

So far, not getting help on my question on whether MH is having external or internal ballast. Which is better?

Another question is what wattage of MH light do I need for a 5 ft tank. Using the calculator in this forum, it came out to be 561 Watt. Isn't it too much.
Gan told me to buy 75 watt per MH and total 150 Watt

Please advise

[Nicky]

Do not know the advantage of having the external ballast other than the fact you can keep the ballast away from sight to keep everything neat.

For MH you cannot use the 3 or 4W per Gallon rule. Just for comparison I keep a 6x2x2ft and only use 2x150W MH and that is already plentiful. Tried 3x150W and was having some problems with algae.

[sherchoo]

For a 5ft tank, 2X150W would be good enough IMO. Alternatively, you could use 4X70W (no 75W) which give you a lower wattage but a good coverage.

I would advise to use 2X150W as this config has higher wattage and lower cost.

With regards to ballast, it really depends on the design of the lighting. There are some originally has it's ballast mounted internally making the whole fixture heavy. Mounting should be given more considerations. But with the ballast mounte internally, you don't have to allocate space to hide your ballast.
With the ballast connected externally, the lighting fixture would be much (and I mean much) lighter making it possible for a pulley system to be installed.

Hope I've answered your question.