I haven't heard anything about the screw in type bulbs. I would assume they would be adequate for such a small tank though. You could always try one and if it's not bright enough add a second. Mentioning that also reminded me of another option. There are desk lamps that use PC bulbs and if you are not opposed to having an open top you can take the hood off your tank and just extend the arm of one of these desk lamps over your tank. It is a little unorthodox, but if you get a nice lamp it actually can look pretty cool. The head of the lamp is long and narrow like a PC bulb so you can center it lengthwise along the top of your tank and it looks pretty decent. Finding one of these lamps that is the right size and looks good will be the hard part though.
As for plumbing your nano into your existing system, there are pros and cons to both. Personally, I am pretty lazy, so plumbing it would be great because I could slack off on water changes, tests, etc. The con would be the chance of contamination of both tanks with disease, out of control algae, aiptasia, etc. Also an overflow box in a little 5g tank might take up a lot of room. But if you do decide to plumb it, you might as well go all out. Upgrade your sump and skimmer, etc, and add a frag grow out tank, a seahorse tank, an aggressive tank, a frogfish tank, etc :wink: . That would be awesome. But seriously, with a small body of water like that plumbing it into the main system could make maintenance a lot easier. Although doing a weekly 10% water change on 5 gallons isn't exactly tough either. Good luck with whatever you decide to do.
P.S. Why am I the only one replying to this thread? Now if something goes wrong it's all my fault
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