Lighting for 20g long tank with retrofit kits

[tanker newbie]

right now i have a 20g long tank, the fixture is 30 inches long * 2.5 inches(at the top of the fixture) and 3.0 at the bottom of the same fixture
im looking to upgrade my lighting and i was looking around on the net and i seen 2 kits that i think would fit me good,
first off is a 30 inch long smart light 6 inches wide and 4 inches high that does 65 watts with a fan cooled fixture for about $120
but now i just found a retrofit kit thats a smart light 55 watt 23 inches long 2.2 inches wide and 2.5 inches high for about $75
i have never had any experiance with retrofit kits and i THINK (not sure thats why im asking) that all i have to do is take out my lighting from the fixture i have now and screw in the reflector of the new retrofit kit, now i just wanted to see if its that easy of just takeing off the old one and screwing in the new one hooking up the wires and turning it on
thanks in advance
allan
p.s. which one would u go with( if i get the 65 watt set up then i would have to get a new custome hood, with the 55 watt i wouldent(i dont think)

 

[fixitdude2001]

I would go with the retro, but what you are talking about will only give you better than 2. 5 watts per gallon, That will limit you to what you could properly take care of with lighting, what do you want to have in there?

 

[tanker newbie]

well right now its a fish only with live rock, however someday i might just get 1 ammone(thats it, just 1) so for 1 ammone a few small inverts(shrimp, snails, crabs) the major reason why im getting it is due to the ammone and to promote bacteria growth on the live rock(20 watts stock just aint cutting it)

 

[fixitdude2001]

Ya I bet, if this is all it would probly be OK but I tell ya what if you could go with up to 5 watts per gallon I think you will be happier , I always said just this and no more but you will see something you like and wish you had more, just my opinion, I am running 10 watts per gallon and looking for a more intense coral to take care of , also the retro kits are easy just make sure you order the right size, for your hood, I made my own,,,cya

 

[tanker newbie]

so far it looks like im gonna be going with the retro fit kit thats 23 inch smart light(50% white 50% antic blue) unless anyone can find something thats more wattage and will fit in the curent fixture