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I have an 18T tank that I want to start planting this week but I don't know what lighting to get. I have an incandescent hood and I have two choices for lighting (screw-ins). One is 25W Philips Marathon 2800K and the other is a generic brand from Home Depot which is 19W and 6500K. Which one is better? The Marathon bulbs are stronger but have a crappy spectrum compared to the other brand's. Does the spectrum matter more than the number of watts?

The most demanding plants I plan on planting are:

Rotala indica
Ludwiga repens
 

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The Marathon would probably be very unbalanced towards the red compared to the blue, which would lead to longer spindly growth, the 6500K would be more balanced in red and blue and in reality, might have as much intensity as the marathon.


Myself, I'd go with the 6500K, but that would be an opinion, semi-literate and highly personal
 

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go with the 6500K definitely, You'll get an apple juice like light from the phillips buls (Very yellow).
 

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Go with the 6,500, no question about that.

You are obviously trying to go the cheap route. But that's not always possible in this hobby, hehe.

These 19 watt bulbs emit a lot of heat. Your (I assume plastic) hood is very likely to melt. It has happened to a member of our club, and she was using the 13 watt bulbs.

Another problem may be that the hood can't accomodate the 19 watt bulb - it's diameter may simply be too big.

Just a week ago I made a hood for an 18T tank. I used galvanized tin - 90 degree angled pieces (used for roofing I believe) and porcelain sockets. Two 19 watt spiral bulbs + two 13 watt spiral bulbs make the hood hot but not smoking hot. I think that plastic would indeed melt - I can hold my hand on the hood for no more than 3-4 seconds :D .

So if you insist on the spiral bulbs either find/make another hood or carefully try and see for yourself if your existing one will work.

I'd say that a better alternative to using the spiral bulbs is to use 2 or 3 normal output 18 inch fluorescent tubes (each one is 15 watts). The hardware to rig 3 of them should not exceed more than $30, but the bulbs themselves may be more expensive if you choose Coralife 10,000K ($20-30 each). Home Depot sells 18", 15 watt bulb that is meant for growing plants (5,000K if I'm not mistaken) for about $8. There are 2 or 3 such bulbs that HD sells, but check different HD locations because their stock differs. You may be able to end up paying about $50 for bulbs, ballasts, and end caps.

--Nikolay
 
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